It's not just slang that causes misunderstandings when you travel . Brand names can be tricky. I bought a bike in England and got those foam handlebar covers for it. When I asked if there was an easy way to put them on The shop keeper said "Just use fairy liquid." I thought he was being funny so replied "Oh good, and the elves will come and do it for me." It turns out that Fairy Liquid is a common brand of dish soap.
Any other examples?