My favourite personal verbal blunder:

Several years ago, I was at my girlfriend's place and she had invited one of her friends over (a girl). I hadn't seen her friend in a few months, and so immediately noticed that her nose looked completely different. I immediately snapped "wow your nose looks really great! superb idea to have plastic surgery!". Which it didn't (ie. didn't look great), I was only being polite and blabbering the first thing that came to mind. The girl's reaction: "I fell off a horse".