My former flatmate tried that on me before - telling me false names of things in Polish. I don't think I ever fell for it, although I was a bit sceptical about a few words that turned out to be true, just because I detected a slightly smirk. The last time I said anything along the lines of...
kapusta was tits in English. Mushrooms were pussy and bigos was cock.
I kept my honesty, if not my modesty and made no mention of cabbage.