If you wear a T-shirt featuring rude words, bombs or cartoon guns you can be prevented from boarding a plane in UK airports.
(Brad Jayakody, was wearing a Transformers T-shirt, which showed a cartoon character holding a gun. He was stopped from boarding a flight by the security at Heathrow's Terminal 5. Better not wear a T-shirt with a frying pan either, Tom and Jerry reek havoc with them.)