Reddit reviews A Barrel of Laughs, A Vale of Tears

Good Omens, about an angel and demon trying to avert the apocalypse when the Antichrist is accidentally raised as a perfectly normal 10-year old would fit.

If you don't mind children's fantasy, A Barrel of Laughs, A Vale of Tears is hilarious.

Would also second Douglas Adams.

A barrel of laughs, a vale of tears?

Here's one you actually may not have heard of/considered: A Barrel of Laughs, a Vale of Tears was my favorite book when I was an ickle teense. I thought it was pretty much the funniest thing ever written.

Not sure how old I was, but I'm pretty sure I was single digits.

I think the funniest book I've ever read was a parodic fantasy: A Barrel of Laughs, A Vale of Tears by Jules Feiffer (who also illustrated The Phantom Tollbooth, another children's comic fantasy, though the focus there was more philosophy than humor). You can get through it in an hour or two if you want ideas. It took tropes and cliches that were noticeable even as a kid (of course the prince needs to save the maiden! Oh wait, that didn't work?) and was just generally irreverent with them. Solutions to problems didn't have to make sense on all levels of logic, but if you squinted right... e.g. The forest gets deeper as you walk forwards - better walk backwards to escape!

With an older audience that reads a lot of fantasy, you can probably drop a bunch of small details from books and it will probably be funny to someone (e.g. braid tugging intensifies, the only music available is Queen, etc).

If you just want to poke fun at a bunch of common tropes, TVTropes or The Fantasy Novelist's Exam might be good starting points.