(idea) by bol Tue Jun 12 2001 at 17:10:27
Apparenly, a chimney is Nothern Irish slang for a black eye. So presumably the singer is asking how pretty the other girl is going to be when she sticks one on 'er.

Eddie Bannon has a wonderful line about this:

"What's she gonna look like with a chimney on her?

"Uh, a house."

I like it!