When a girl takes a dump in a freshly cleaned porta-potty and some blue liquid splashes up onto her vagina and a guy gets it all over his face after going down on her.
You'll know a blue beard when you see it.
A person, usually male, with multiple partners.
A player, or not.
You shave off a read beard and become a blue beard.
I dumped his sorry arse after I found out he was a blue beard.