Two of my favourites that I stored up to use in anger, and succeeded fantastically....

to a boasting colleague 'congratulations, what do you want, a medal or a chest to pin it on?'

and to same colleague boasting about his sport/sex life 'Ooh, you sound like a real action man, flock hair and no genitals'.

The second retort had me fishing a colleague out of the photocopier from whence she'd collapsed laughing.

LTS