A more gratuitous derivative of the simple Your Mom, in which someone describes having sexual relations with another's mother in an attempt to offend or shock them. While it almost always used either sarcastically or as a form of trolling, it can also be found being used by typical players in online gaming matches who have decided that actual insults simply did not display their rage thoroughly enough.
Never, ever used with any sort of context.
Player #1: No! What are you doing!?! You're letting them take the fla-