I was driving my bus the other day when a guy got on with a tin of paint. Regulations here in the UK state that such items must be contained in a second container such as a carrier bag, so I told him.
"It's okay, I'll put it under my mac." he said.
"You can't do that, it's gloss!" I replied.
"What difference does that make?"
"You can't use gloss as an undercoat!"
[For Americans' sake, mac = mackintosh, a coat - ed.]