I love jokes about farting. Just the word "fart" makes me giggle. This used to embarrass the heck out of Mr. Mausburger when we first started dating. He has adjusted and tells me lots of nonsense joked using the word "fart." Even now, when I talk about poop (digestive problems, toilet paper, etc) in polite company, he still gets uncomfortable, but rolls with it.
A story on the BBC reported that the world's oldest joke is as follows:
Something which has never occurred since time immemorial; a young woman did not fart in her husband's lap.
This was found in Sumeria, now Northern Iraq. The funniest joke in the article is about the Egyptian pharaoh. More examples can be found on a recent MetaFilter thread. To this, I contribute my favourite pharaoh joke.
"I have some good news and some bad news," the galley master of the Royal Barge told the rowing slaves, chained to their oars. "The good news is that today's gruel ration will be doubled. The bad news is that the pharaoh wants to go water skiing."
I don't know where this came from, but I'm pretty sure there's a Far Side cartoon to go with it.