Yona writes that "there is a great deal of literature on verbal violence/abuse, and 90% of it indicates it's a lost cause and your best method for dealing with it is to cut and run (see Patricia Evans' _The Verbally Abusive Relationship_ and many others.)"
I agree. The problem with the verbal violence/abuse literature is that almost all of it completely ignores body language -- including ignoring intonation and tone of voice, which are the most powerful parts of body language for English. The Evans book doesn't even have an entry for those items in its index. People are instructed in these books to say things to verbal abusers like "I will not put up with that sort of talk"; that's called "setting limits" or "establishing boundaries." Nowhere in the books do the authors point out that "I will not put up with that sort of talk" (and all the other proposed utterances of that kind) can be spoken in a host of different ways, some of which are likely to put the speaker in danger of physical abuse as well as verbal abuse.
This situation is caused by two factors. (1) Authors who are native speakers of English and not trained in linguistics often take it for granted that the sentence they "hear" in their mind as they write their words down will be "heard" by the reader in exactly the same way. This is a dangerous assumption, and rarely accurate. This is what makes printed lists of "Things to Say When...[X]..." so dangerous. For English, speech quoted in writing is naked of its emotional message; the emotional message is added when the words are said aloud, and there's no way to guarantee that they'll be said the way the writer intended. (2) Even when authors are aware of this problem, they have to fight their book editors for permission to use unconventional punctuation as a way to get around it. In my verbal self-defense books I write my examples like "WHY are you leaving early??!" and "Why are you leaving EARly?" and "Why are YOU leaving early??" and so on, to give the readers some clues to the emotional messages carried by the words. But I have to fight my editors for permission to do even that much, every single time. Editors _hate_ unconventional typefaces and punctuation; if the author isn't willing to really get in there and insist, all of those sentences will appear in his/her book simply as "Why are you leaving early?" That's absurd, but it's the way things are in the real world. These authors shouldn't have to take full blame if their editors refuse to let them provide these graphics clues, especially for a first book. They _should_ be blamed, however, for not providing a page or two explaining the importance of intonation, tone of voice, and other body language, and cautioning their readers about what can happen when the wrong tune is attached to one of their suggested utterances.
When books on verbal violence/abuse provide their suggestions for English speakers with no attention to body language, the results people get from following those suggestions will often be extremely bad. Which is why the authors do, as Yona says, tell you not to have high hopes; they base their predictions on past results, which -- with no attention to body language -- will not have been reassuring.
Mary S writes to suggest saying something along the lines of "I find it frustrating when I lend items that are not returned. Perhaps we can sit down and discuss what can be done so I don't feel this way." When she wrote that sentence down for us, she "heard" it in her mind's ear with a particular tune, one that carried the emotional message she wanted understood by a person hearing it aloud. Unfortunately, we can't tell by looking at the words what that tune was. Was it: "I find it FRUStrating when I LEND items that are not RETURNED! Perhaps we can sit down and discuss what can be DONE so I don't FEEL this way!!"? Was it: "I find it frustrating when I lend items that are not returned....... Perhaps we can sit DOWN....and discuss what can be DONE....so I don't FEEL THIS WAY???" Was it one of a dozen other possible ways to say those words? We can't tell.
I'm not criticizing Mary S -- not at all. She is writing as all of us have been taught to write English, and has done absolutely nothing that can be criticized. The flaw is in the way we're taught to write English, and the way we're kept ignorant of the fact that written English is an impoverished medium for sending emotional messages.
There's a useful device for stating complaints that originated in something called an "I-message," was developed by Thomas Gordon into something called "a three-part assertion message," and then got a bit of tweaking from me to produce what I call simply a "three-part message." This pattern has proved extremely effective as a way of changing behavior -- not a way of educating, or raising consciousness, etc., but as a way of changing behavior. Part One of the three-part message states the exact item of behavior you want changed; Part Two states the emotion you feel about that behavior; Part Three states the consequences of that behavior that provide you with justification for making the complaint. (If and only if no consequences can be stated, a statistic can be used as Part Three.)
Everything in a correctly-constructed three-part message should be concrete and verifiable in the real world. (Part Two is the weakest part in that respect, but should still be verifiable in the sense that the emotion stated is backed up by body language and context.) Ideally, nothing in the message will be anything that a reasonable person could argue with.
Suppose your housemate has promised to water your tomato plants and you've come home and found that he/she didn't water them. Here's a three-part message for that situation: "When you don't water the tomato plants, I feel angry, because plants die without water." Part One ("When you don't water the tomato plants") states the behavior that you want changed, and an observable fact in the real world. Part Two ("I feel angry") states your emotion, backed up by your body language and the context. Part Three "(because plants die without water") states the consequences of the behavior you're complaining about, and an observable fact in the real world. If your housemate is especially touchy and defensive, the message can be put into Computer Mode to preserve face, like this: "When the tomato plants don't get watered, people feel angry, because plants die without water." You have to say your three-part message neutrally, however. If you say it sarcastically or patronizingly....if you say "When YOU don't water the TOMATO plants, I feel ANGry, because plants DIE without water!!!".....a three-part message will work no better than any other confrontational utterance.
Can we re-write the utterance Mary S suggeste, as a three-part message? She suggested this: "I find it frustrating when I lend items that are not returned. Perhaps we can sit down and discuss what can be done so I don't feel this way." We'd begin with "When I lend you a book and you don't return it, I feel frustrated, because....." That leaves the third part -- the real world consequence that justifies making the complaint -- to be filled in. Only Mary S can know what the third part would be. Some possibilities: "because I have to go to my economics class without my textbook"; "because I can't start my term paper without that book"; "because 37% of all borrowed books that aren't returned within three days are never returned." (I made up the statistic for the example -- so far as I know, there's no such statistic.) In Computer Mode: "People who lend books and don't get them back on time feel frustrated, because...." or "When somebody borrows a book and doesn't bring it back on time, people feel frustrated, because..."
The track record for three-part messages is very good. I recommend them. It's wise not to tamper with the pattern -- it's not broken, so there's no need to try to fix it. And when you find that you can't come up with anything to go in the Part Three slot, that usually means that the problem is not with the person you want to complain to but with you yourself; that's useful knowledge.
Finally, about the "Perhaps we can sit down and discuss what can be done so I don't feel this way" item. I don't recommend that as a general rule, although there will be situations when you know it's the appropriate thing to do. For one thing, people who use abusive behavior as a way of getting attention will be thrilled with the opportunity to sit down with you and talk at length, as suggested; you're rewarding their abusive behavior. For another, your three-part message is your _move_ in the situation; once you've sent the message, it should be the other person's move. If you add "Perhaps we can sit down and discuss what can be done so I don't feel this way" to your three-part message you confuse the situation, because you've moved twice instead of once and have given the other person no opportunity to respond in between. You can always say that later if it turns out to be appropriate.