A poo bender is the act of dedicating a night out to poo'ing and in particular poo'ing hard. A poo bender can take place with ones self and a handful of laxatives or can be shared by friends a family in a more communal way.
Jon: Hey guys, did you hear Alex's is hosting a poo bender!
Scott: Yeah, hell yeah!
Sean: Ive got the laxatives someone grab the stools!