I can’t believe you served Buffy that beer.

Giles: I can’t believe you served Buffy that beer.
Xander: I didn’t know it was evil.
Giles: You knew it was beer.
Xander: Well, excuse me, Mr. ‘I spent the sixties in an electric-kool-aid-funky-Satan groove.’
Giles: It was the early seventies and you should know better.