I was in a hardware store in the plumbing section with short length of threaded pipe in my hands flipping it over while thinking of the best way to make something work with the parts that they had.  A cute salesgirl comes over and asks me if I need a hand.  I say "No thanks, I'm just fiddling with a nipple."  Short embarassed pause when I realize what I had said, and she just looks up and smiles and says "That's what they're for!"  

 Same store, different day, different girl working the cash.  After buying a couple of pounds of screws, she wishes me "Happy screwing!" as I leave.  Half a second pause and then she and the other cashier just about die and drop down behind the counter laughing, one with her face beet red.  Gotta love people with a sense of humour!