'Only someone who'd gone to university could be that stupid.' - Funny because it's true. Usually used to describe right-on lefty students who call Bush 'worse than Hitler' and Saddamm 'an underrated diplomat.'

'I'm hurt! Call me an ambulance!'
'You're an ambulance!' - A classic case of wordplay in the tradition of Barker, Corbett, et al. Here, we see how the request is commandeered in the pursuit of comedy, transformed into a surreal retort which is funny for two reasons: 1) It's witty, and, 2) The person being called an ambulance may well be bleeding to death as said witticism is being delivered.

Your own, with analysis?