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.
In the process of courting a young lady you try your luck by moving your head in the direction of her lips. This act usually occurs at the end of a social night. This may result in a "Shift" or a "slap" both of which you can "chat" to the boyz about.