When someone is getting fucked in their shitty asshole, they may proclaim this state of discomfort.
Rubbercow got some hot anal and said "Oh my ass". Ed masturbated.
by Seifer Almasy June 27, 2003
More vocal than anything, Oh my ass is a declaration that you are getting fucked in the anus by a large wanger.
Raven watched as Seifer put it in Squall deep. He screamed "Oh my ass!"
by GhaleonX July 23, 2003