I pushed it once on a DL flight last year...I was stuck in coach, and all of a sudden the girl sitting next to me was creeping into my space. I ask her what's going on, and she points to the aisle and says "that kid across the aisle threw up and I don't really want to be near it." At that point, I hit the call button, the F/A comes down looking a little annoyed (since it was around midnight on the delayed flight) and I just pointed down to the floor and she knew why I hit the button. That's the only time in the 20 years/150,000 miles that I've travelled that I've hit the button.