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.
popular in the so-called "Triangle" area (that's Ballymoney, Coleraine, Portrush). used instead of "mate" e.g. "'bout ye sham" meaning "how are you mate?" Often claimed as an Ulster-Scots term. Ulster Scots is a "language" that has been spoken in Ireland for almost 10 whole years now.