A condition affecting about 1 in 20 humans that results in an upside down hard one when experiencing morning wood. Usually comes from having a sex change two or more times, and normally occurs on tuesdays.
Tim: Hey, I saw Scott Chubbs in the gym toilets this morning and he had an upside-down pepsi.
John: Did you kick it?
John: Shot bay. I always knew Scott chubs used to be a girl.
Tim: Yea, but that upside down pepsi was upside down! I thought they were a myth!
John: Na G Tim: Oh, aye G