"Red flag" has become a
slang term in
schools (at least where I Live) meaning "watch out, this
kid might go
Columbine!". Someone must have seen it on some
TV show or heard it on the
intercom or something, and it just
caught on. It implies, in jest, that this is a potential problem (in the sense that
jonlasser was talking about) and the offender ought to be
referred to the
authorities. You say it when someone makes an offhand, joking threat of violence . For example:
"I'm getting a C in biology."
"Haha, you're an idiot."
"I'll kick your ass."
"Uh oh, red flag!"
I guess it makes one realize just how common a device this in in conversation, at least among hormonally driven teenagers. It's also a somewhat embittered shot at a system that now thinks everyone in this country is liable to fly off the handle just because they threatened to kick someone's ass. Lighten up, America.