the multiple meanings of "fly"
I was sitting in the hall before class last night, waiting for the room to empty. As the kids from English 1B filed out (read: "second semester freshmen") and I was getting up from my position on the floor, I noticed one baggy-jeans'd boy had his fly down. I quickly accessed all that I could recall about current fashion trends and was comfortable in my assumption that regardless of prevailing trends, if your fly is down that's just not good.
So I said "Dude, psst" and he looked over, surely wondering why the old person on the floor was trying to get his attention. "Fly," I said. He looked all embarrassed—as he should—said "thanks," and kept walking.
Confused, it wasn't until he had made the turn down the hall that I realized in his little self-absorbed world he had to have thought I meant "[you are] fly" (which he decidedly was not) when what I was trying to convey to him was that he was one step away from inadvertent willie-waving.