A few years ago when this boy from my school just turned around and said, ever so seriously, "You might be really smart, but you're also really ugly." It was one of those "people in glass houses" situations, and i threw it right back at him - "i may be ugly, but at least i'm not fat and ginger!!" (okay, but i am immature)
And when my dad's gf and i got into a fight, she said that i was a "manipulative bitch" - that's rich, coming from the festering tart who ruined my parent's marriage. She later apologised, but i've never really forgiven her for it.