the buildup of seminal fluid from jacking off in the shower that prevents the shower from drainng.
beacuse of the fuckin cumblock the shower takes four fuckin hours to fuckin drain
The act of walking in on your mate or male having sex with their girlfriend/wife as they are about to cum or nearing the stage where as they would usually cum. Thereby preventing them cuming. This is also similar to the legendary Cockblock.
Sam: Dude I can't believe u Cumblocked me I was so freaking close arr.
Rory: Im sorry man, how could I know?
Sam: Well walking in for a start would have helped!!!.