The Dread Portal scene in G!G!.
NO SUGAR PIGGY WIGGY FOR YOU, ALBERT.
Detritus & the Alchemist - 'Ere, you loony bastard, what you make of this ?' Cracks me up, every single time.
Nanny having a bath.
My possible favourite of all though is from Soul Music;
'I can blow anything,' said Glod.
'Really?' said Imp. 'That must make you very popular.'
There's lots of bits that I've laughed myself sick over though.