To continue jacking off after ejaculation.
Henry: "Yeah bro me and my friends were all sitting around a fire, just beating the dead horse!"
Joe: "Be careful man! If you beat the dead horse too much you could get a 90 degree angle cock from that!"
Henry: "You only get one life joe, live it up."
An instance in which the "beater" of the horse will continue to try and make amusing comments until either
A.) Somebody makes a "pity laugh" (this is usually the person who originally told the joke) or:
B.) Everyone leaves.
This is a common occurrence when a moderately funny person loses their game, and is convinced that they are not off of their game.
The perfect example of beat the dead horse.
MD: "Yo wassup homeslice! I was just chillin like a felon up in hurr."
OM: "Oh, awesome."
MD: "Word it was so tite and of the hizzle son! Shit!"
AS: "umm cool"
MD: "Damn staraight Gangsta. I'z with all ma peeps."
JK: "thats great..."
MD: "You know what else is great? My dick!" (MD laughs at his own joke, hoping others will too.)
WH: "shut the hell up mark youre not funny"
JB: "Whack! Whack! Whack! Neeeiiigh!!"
MD: "Peace out haters"