I agree that there isn't a rule specifically adressing this but I definitely consider yelling at a player shooting a layup an unsporting act. However, I would probably talk to the player when I had the chance and tell them not to do it again rather than give them a 'T' right away. Since this situation usually only happens once maybe twice a game I may let the first one slide and then talk to them if it happens again, but I don't think this warrants a 'T' right off the bat.