When a naked standing man pours a beer down his chest and the recipient chugs it as it cascades off of the mans cock.
Andrew: Mike, why are you naked and soaking wet?
Mike: Because I'm awesome... and I Just got done giving this whore Diana a cock bong!
Alternative phrase for the more commonly used "penis pump". This is due to it's resemblance to a bong, and the fact the penis is placed inside said object.
That's a cock bong man, you must have a tiny wanger.