like the back of a bus
Particularly ugly, unattractive, or sexually undesirable. Primarily heard in UK, Ireland. Many people in this profession still hold the view that if you don't have a face like the back of a bus, you're only getting ahead because of your looks. He looks like the back of a bus, but he's a really sweet and intelligent guy.
like the back of a bus
(of a face) very ugly. informal 2004 Waterford News and Star What's so great about a guy that has rotting teeth, lungs of tar and bless the poor bloke but the back of a bus does him fair enough justice.