Brad Jayakody, from Bayswater, central London, said he was "stumped" at the objection to his Transformers T-shirt.
Mr. Jayakody, a clean-shaven young man with eyeglasses and short hair, said the incident happened in mid May, when he was challenged by an official during a pre-flight security check.
"He says, 'We won't be able to let you through because your T-shirt has got a gun on it'," Mr. Jayakody told reporters.
"I was like, 'What are you talking about?'
"(The goon's) supervisor comes over and goes, 'Sorry, we can't let you through and you've a gun on your T-shirt.' "
It wasn't even loaded!