Someone who betrays you in a way that profits them, but leaves you out in the cold. They could have acted as you friend or loyal business partner initially, but took an opportunity to screw you over royally.
A person that hides inside a toilet waiting for a victim, when someone puts his/her butt on the toilet the buttsucker lunges for his/her butt and sucks all the crap out.
You can't leave the toilet seat when your buttsucked, because the power of the buttsuckers sucking is superb.