I would recommend Rat Race over Mad Mad Mad Mad World - the plots are similar, but I find Rat Race much funnier, personally.
Brazil (more weird than wacky but definitely different) or Hey Dude, Where is my car (basically so stupid its funny).
Agreed. M[sup]4[/sup]World has the edge if you get a thrill out of identifying old movie and television stars of the first half of the 20th Century, but Rat Race is definitely funnier.
EDIT: linkified (directly to the Watch Instantly page)
Don’t know what edit of Brazil you’ve seen, but Terry Gilliam’s cut utterly devastated me the first time I saw it, with me sitting in my seat utterly poleaxed as the lights came up after the credits.
I consider it my favorite film of all time, but I don’t consider it “wacky”.
Dude, why do you think I put the weird caveat in there? And it is wacky in a way until the very end (who couldnt like handyman ninjas?) when you figure out whats really going on and then it is sucky depressing.
Thanks for the suggestions (and keep them coming!) I’ve seen several of these but there are plenty that I haven’t (and like The Big Lebowski, I’ve always meant to see but never gotten around to!)
Today I ended up actually watching a DVD of Black Books episodes, but tomorrow I want to see something I haven’t already watched a thousand times 
I’ll seventhed Big Lebowski, Role Models and Hangover.
I had no interest in seeing Hangover even though I love Zach Galifianakis stand-up routines and I was suprised at how funny it was.
Yeah I have already seen the Hangover. It was funny 
Haven’t seen the other two.
I still don’t think it fits the OP criteria at all. It has some very funny bits, but the humor is generally pretty dark at best, and definitely not “wacky”.
I’ll save you the debate and point out that I’ve seen Brazil a few times already
I and the vocabularly challenged thank you. Now, go rent Dude, Where is my car?
I could be wrong, but I don’t think Opalcat was agreeing with your description of Brazil.
Yeah I was just saying don’t argue about it since I have already seen it. Also already seen Dude, Where’s My Car.
She? said she would save the debate because she has seen it ALREADY, so it doesnt matter whose description is more correct. Work on your reading comprehension skills some too sparky. Heck, I don’t agree with what some others here are calling “wacky” movies but you don’t see me getting bent about it do you?
Oh, and along the lines of “Wacky”, apparently trade marked by the Gaffa OCD corporation, Harold and Kumar Go To Whitecastle is about as fun and “wacky” as Dude, Where Is My Car?.
Oh, and there is a movie where a mormon missionary becomes a porn star/hero of sorts, but the title escapes me at the moment…
The Emperor’s New Groove - wacky, very funny - just about the best Disney movie out there.
mormon movie…Orgasmo, I think (also co-starring Choda boy)
Seconded! I adore The Emperor’s New Groove. Funny, smart, and strangely sweet at times.
Also seconding wheresgeorge04’s recommendation of Idiocracy. It’s not everyone’s cup of tea, but I love the hell out of that movie.
I would like to register a complaint to those who recommended Role Models: I was all jazzed to stream the movie when I got home…but noooooo, it isn’t available to watch instantly!
Ed Wood (not sure about instant Netflix availability though).