a follow-on term from the word bant. If someone is a bantsponge it means they are no fun, i.e. they are 'soaking up the bant'. yes its cheesy but we love it.
Fred: Here's my globe Jed, clearly the earth is not flat.
Jed: Fuck you Fred! I know you and your sisters cousin's uncle made that globe from communist drawings you found in George Clooney's mansion after he paid you to spank him while wearing women's panties!