One game we found a 10 foot tall stump that was hollow. We placed a sentry up there with a Mac 11 to cover our base. Some poor fool ran up, used the tree for cover and got shot right on top of his (bald) head.
My favourite was when a teammate squatted down in the middle of a firefight to answer his cellphone and talk to his GF for like ten minutes. Whilst returning fire . . .
"Yeah, though I walk through the Valley of the Shadow of Death, I will fear no Evil, for I am the meanest son-of-a-bitch in the Valley."