Wow, there's about 300 great moments to choose from. I don't know why, but that "Revenge of the Killer Surfboarding Bikini Vampire Girls" (um, bit of an approximation there) scene from 'Legion' springs to mind. I find Lister's cunning double to be hilarious.

Otherwise, Rimmer's explanation of why aliens have broken legs, done jigsaws etc. is great.