1. Usually occurs when two males are involved in a threesome with a consenting woman, and one of the men inadvertently sperms on his buddy while the act is taking place. Is most severe when the victim is hit near the head or the butt hole, in which case the threesome usually ends. Usually occurs during a switch or swap. Can happen in a threesome involving all women, provided they are potent squirters, in which case it will usually be rubbed in by the recipient and the threesome will ensue with even more intensity than before.
Just as I start to go to browntown, Ben freaks out that our balls were close too touching then ends up losing it all over my thigh. In all my years I never thought that I could be a victim of friendly fire, it's just one of those things that you hear happens to other people, like your uncles or something. (Excerpt from Fred Savage's autobiography "Sex With Granpa"