a crusty bag is when a male puts his testicles in a large bowl of chocolate, waits for it to set and starts smacking it on the womans face so it starts to crack then anouther has too lick it off whilst its happening.
"hey, girls you want to come over and try my crusty bag?"
a sack of testicles that havent been washed in a while and are starting to get crusty
sawyers testicles are a crusty bag