Ioan Gruffudd & Alice Evans #156 No one is responsible for Alice's bills but Alice.

[AuroraBorealis]

buttocks, backside, bottom, behind, seat, rear, rump, rear end, cheeks, hindquarters, haunches, derriere, Sitzfleisch, nates, sit-upon, bum, fanny, gluteus maximus, keister, posterior, tail, tush, duff, buns, booty, caboose, Heinie, tuchis, bazoo, bippy, batty, rass, fundament, breech, arse, clunge, backside, stern, prat, tail-end, patootie

Perhaps rass then? So it would rhyme with class.
(I understand it was about the thread title suggestion by Buttertart and Invictus early in this thread.