"However I'd like to ask you if you think a group of kids, forget the color, continually taunts adults on the street, then could they themselves get braver and more aggressive as their experience builds until they cross a line and do something outwardly stupid?"
My answer is twofold: one, if they did, it's only a matter of time before the cops round them up, and two, I've NEVER seen a group of kids TAUNT adults, particular a dude and his family. If I may interpret and apply what Konrad Lorenz discusses in "On Agression" (I'm reading it now. It's very informative), if you were to give the group mind some sort of animal designation, then the animal mind would only attack something that was of the same or very closely related species it thinks is on its turf, i.e., another kid, or particularly a kid that one of them does not like. The only trouble I've heard of adults having from a group of kids is them relating the story to me of how they survived an attack. Bottom line is that if there had really been an threat there, with the odds at LEAST 2 to 1, in the kids favor, and no one else was around, John C's post would have started off with "Let me tell you how I got ATTACKED" in DC. In addition, if he really did avoid a confrontation, there wouldn't have been ANY laughter afterwards. That particular type of group would be behaving in predator mode, and I'm sure they would have seized the opportunity to circle and attack perceived prey (i.e. John C and family) ESPECIALLY IF THERE WERE NO WITNESSES. However, I will say again, that unfortunatetly, if you put out the "I Am Afraid You Will Attack Me" vibe, some idiot WILL. It's a self fulfilling prophecy. I stay AWARE, but I don't stay AFRAID. (This is coming from a guy who has TWICE had a group of teenagers try to stone him as a child when he was once with his mother and cousin, and again, when he was with a playmate, by suburban children!! Let me remind you that this was NOT in the District, either!!!!!!!!)
From what I gathered from John C's post, those kids were probably a normal bunch, bumming around, going to catch a movie or something, particularly at that time of night in that local. I really did not perceive any taunting at all, from the facts as he has relayed them. Teenagers are (forgive me please for generalizing any teenagers reading this, but if you look at how you treat the geeks in your school you know it's true) are some of the most cruel, NON-compassionate people on the planet, regardless of race. In fact, they'd probably give someone in their own race a razzing more so that an "outsider" (per Konrad Lorenz and what I've seen myself), because the "outsider" is outside of their perceived territory. As ANY adult would most likely be, UNLESS THE KIDS WERE PREDATORS ON THEIR OWN TURF. I really don't think those kids were predators. Now had it been WELL after the Metro rail should have been closed and there was no real reason for them being in there, then that's a red flag. Also, these youngsters were OUTSIDE OF THEIR TERRITORY. If a group of kids in a group-animal mindset, (like what Lorenz discusses) is in their territtory then there may be some concern. The metrorail system is considered a neutral territory, particularly outside of the district itself. I take the rail all the time, so I know.
It's really rare that something happens on the trains. John C (and most tourists and travelers) should be more worried about terrorist attacks and the bomb threats that happen in the federal section of the town, rather than a threat from the locals. (Believe me, judging from the onslaught of camera-carrying father-son and mother-daughter pairs that mob the city every spring and summer, asking us poor people going to work where the Washington Monument is, like you can't see the darn thing as big as it is, from any hill in the tourist section, I don't think the visitors feel threatened or ARE threatened.)
I would say to go into a yellow zone of awareness around the tourist part of town (am I quoting Van Canna with that code yellow thing??) just to be safe.
Enough said by me. I'm tired and I want to go home so I can go catch the Star Trek premiere!!!!!! (Duhn, dun da duhn, dew da duhhhhhhn......)
P.S. Okay, so I'm a Trekky, but just for the record, I've never been to a convention. Really. Honest.