Someone doing something that they shouldn't be doing e.g. a ref giving a bad decision at a game, a child playing with a box of matches, a garda pulling up someone for pissing in a dark alley etc.
I'm almost finished with Robert Ludlum's novel THE ICARUS AGENDA, which has two slang phrases in it that have me scratching my head (a lot). "A two toilet Irish detective" is supposed to be American Boston-Irish slang, and I guess isn't too hard to figure out. I still wanna know!