Dog Latin for "Don't let the bastards get you down." Not real Latin, like Lorem ipsum. It's even on wikipedia, so I'm surprised it's not on UD.
In the huddle:

Lineman: Who's house? Our house? What time is it? Game time!

3rd string QB: Illigitimi non carborundum!

Other Lineman: What the hell was that? Get out, white trash!
by no molesta! December 29, 2010
Get the illigitimi non carborundum mug.