I had a funny instance last night with this actually.
I've been a Gears whore since the new map packs came out, so that is where my gaming time has been spent. We were playing execution on All Fathers Garden and three of the opposing team had just taken out a guy. I don't know why they didn't realize he obviously wasn't the last guy, but they all started face humping him as he was trying to crawl away. I was slightly above them with the boom shot, and yes... I fired one round directly in the middle of them. All three were turned into a fountain of blood and body parts.
My team couldn't stop laughing.
Personlly, if I get tea-bagged, My first thought is "really? I mean... really? Grow up."
I have only ever done it when playing against someone I know in real life, and that was a LONG time ago, back when it was still funny.