Post-Modern Humour is also completely post-modern, and completely different to the examples quoted above:
Post-Modern Humour is essentially the making of jokes that are not funny but work on our sub-conscious through what we expect to happen. For example, here are two very good post-modern limericks, the first by Edward Lear, the second of unknown origin (or unknown to me, anyway.)
There was a young man of St. Bees,
Who was horribly stung by a wasp.
When they asked 'Does it hurt?'
He replied 'Not too much.'
It's a good job it wasn't a hornet.
There was once a gasman named Peter,
Who slightly messed up with a heater.
With a resounding 'boom'
He was gone from the room,
And, as anyone who knows anything about poetry can tell you, he completely ruined the metre.
Similar to this are the people who put '68' on a scoreboard. Whilst the childish thrills of putting '69' are obvious, the only thing going for '68' is that it isn't quite what we were expecting. '66' is likewise explicable for its resemblance to 666, but '68' is completely and utterly pointless. And therein lies the wonder of post-modernist humour.
Albus Dumbledore's speech at the beginning of Harry Potter and the Philosopher's Stone is a prime example. He says 'I would like to say a few words: Nitwit! Blubber! Oddment! Tweak!', which cannot be deemed a logical train of thought by any but the already-mad. However, it is not my opinion that Ms. Rowling is mad, but possessed of a strong post-modernist sense of humour.
In much the same vein, not for nothing do many Monty Python sketches end abruptly. Likewise many start with the by now infamous words 'And now for something completely different'. This is because non-sequiturs are, by their very nature, confusing and disrupt the mind's train of thought, thus requiring the audience, in much the same way as modern art, to re-evaluate what they expect.
This w/u brought to you by the British Council for Spelling 'Humour' Correctly.