Le Dîner de Cons. I have been showing this to people for 13 years and no movie has more consistently produced such loud, sidesplitting laughter. 
Once again, this thread isn’t for listing all your favorites, whether they’ve already been said or not-it’s for listing your one favorite movie, even if it has already been chosen. if you list something only because it hasn’t been said yet, then your real favorite might not make it to the poll.
Caddyshack
Dr. Strangelove, c’mon, people! Funniest movie ever!
For the car chase in costume sequence, Pink Panther.
This is Spinal Tap for the Stonehenge sequence (which I need to rewatch to see if I can show to my third graders to explain the importance of double-checking math work)
One more vote for Young Frankenstein
Annie Hall
Planes, Trains & Automobiles (1987)
*Neal: He says we’re going the wrong way…
Del: Oh, he’s drunk. How would he know where we’re going? *
Monty Python and the Holy Grail.
“The Breakfast Club”
I still crack up every time I see it.
I’ll be one of about three on here who’s seen it, and maybe the only the only one who thinks it was so great.
But for all-around laughs per minute, the speed and timing of the dialogue and hi-jinks in “Bringing up Baby” is truly stunning. I laughed myself silly the first time I saw it at about six years old, and I’ve done the same about once every five years since. Which comes to mumbles times and still helpless with laughter each time.
Going new school:
Old School
Dogma
Want to change mine to:
Animal Crackers
Well, art is art, isn’t it? Still, on the other hand, water is water. And east is east and west is west, and if you take cranberries and stew them like applesauce, they taste much more like prunes than rhubarb does. Now, uh… Now you tell me what you know.
The Big Lebowski
Also:
Bedazzled (original, not the horrible remake)
Team America: World Police
The correct answer is:
A Funny Thing Happened on the Way to the Forum
Hot Fuzz
Top Secret!
Which one?
If a poll were posted with the names already mentioned, I would have to vote for about five of them, but would probably end up with Raising Arizona on some sort of tie-break system I’d come up with.
And even though it doesn’t produce a laugh a minute throughout, I have never laughed harder and longer than at Lee Evans in Funny Bones (1995). The movie suffers from too much Jerry Lewis (as does any movie he’s in) in a decidedly unfunny role. But if you can bypass that negative, it’s a scream of a movie with Evans going places that other physical comics never went. I’d like to see other reactions to this particular movie, if others may have happened to see it.
Anchorman
The Princess Bride
I don’t remember ever having more fun watching a movie in a theater when I first saw this. I’m absolutely shocked that it took 60 posts for this to be mentioned.