Paul Boag on Twitter just asked for suggestions of amusing videos on YouTube. Here are a selection I can think of:

American Idol Season 7 - Milo Turk Performs "No Sex Allowed"
This one was shown (for humour) during the introduction to my YWAM DTS course:

Numa Numa
You can't beat a classic lip-(almost)-sync:

Leeroy Jenkins (Warning, contains F-word)
I actually used (an F-word removed) version of this in a talk about team-work in the youth group I helped at once:

Gimme Pizza Slow
Maybe a tad long, but could become an anthem!

The Realize Movie
Not particularly funny, but thought provoking:

It is funny: I'm sure there are many more funny videos I've seen on YouTube over the years, but when it comes to recalling them, I'm having a hard time! If you think of any, why not post links in the comments here, and let @boagworld know on Twitter too.