Two or more people heading to a communal washroom to go poo. Sitting in stalls side by side they go in unison. If one person should need a little extra time the others will wait with them. They are permitted to laugh if one of the "bombers" lets out a big ripper/ toot!
That coffee made me had to bomb really bad.... "Laci, Amber, Sarah, Christie and Krystle... lets go have a bomb-a-thon"!! ;)