Hmmm...sounds a bit confrontational to me (yes, I know...you're in a confrontation..but bear with me).
One of the things Coach Blauer stress when talking about the verbal arsenal (and in general) is feigning fear and using congruous words and body language.
In other words, don't tell the bad guy that you're willing to fight.
Think about it...if you do have to hit this guy, the last person you want to know about it is the guy you're about to hit. So why tell him?
If, instead, you said "Ok..ok (gulp) I'll give you my money...do you promise not to hurt me?", you've now a) got this guy thinking you're not a threat and b) maybe can get away with handing him your money and leave (if such is your desire). Either way...the guy won't know what hit him.
Telling him you'll fight challenges his ego. It may actually Induce violence (i.e. "Oh, you're gonna fight me? What? You some kinda ka-ra-tee gook or somethin'?")
Interesting story, possibly relevant: A number of years ago, my aunt was mugged on the subway in NYC. She had lived in NYC most of her life, and been spared the general urban violence, but statistics finally caught up with her.
She told her attacker: "Please...I have some things in my wallet which are very important to me. They're totally worthless, but I NEED them for my job (she's a college prof...had ID's and such with her). Let me just give you all my money. I'll give you my credit cards too...but please let me keep my wallet"
Guess what? She kept it. Lost the money, but so what? A minor loss in the general scheme of things.
Now...imagine if right after asking that, she had sucker punched the guy...
Should you practice this scenario in the dojo? ABSOLUTELY! However...I wouldn't force someone to use any particular phrase or wording. Let them develop their own verbal arsenal...then it will be there when they need it.
Food for thought.
Defeat is worse than death. You have to live with defeat - Seal Team Slogan