I did one of them on the elevator the other day in school. I got on the elevator and there were a couple of girls on there. I unzipped my bookbag, peered inside and said, "Do you have enough air in there?" I waited a moment and said "Okay. Let me know if you don't."
I zipped up my bookbag and stood there staring straight ahead. The girls were looking at me strange and I was trying hard not to laugh. They got off on the next floor and I heard them cracking up as the doors were closing. I was laughing so hard myself, people were looking at me strange when I got off on the next floor and they were getting on.
That's good stuff right there. lol.