When one wakes up in the morning and realizes they can't open their eyes because there is dried semen stuck on them. Very similar to eye boogers (rheum).
I was so pissed when my girlfriend wouldn't have sex with me last night, so I jacked off and unloaded a torrential cum storm on her face. When she woke up, she tried to open her eyes, but couldn't cause they were full of man crusties.
The organic matter dried and caked onto the mouthpiece of a bong. Often times bong crusties appear after using the pipe for many days/weeks/months without proper cleaning; also a side effect of too many people sharing one piece.
Dude!#@ Clean those crusties off before you pass The Chuggler. I don't want your gnarly mouth herpes on my piece!