Recently caught a bit of Mrs. Doubtfire and it reminded me of seeing it for the first time in the theater, and laughing out loud at times, most notably at the scene when Robin Williams almost gets mugged and shouts (in his normal voice), "Back off, a-hole!"

It made me wonder: what movie made you bust a gut the most the first time you saw it?

Either Kingpin or Bad Santa.

Parts of Rush Hour 2 for the first time in the theater (one guy in front of me literally fell out of his chair) and the first Anchorman on opening day immediately come to mind.

In general, I remember losing it watching There's Something About Mary. I was only 12 when that came out but I convinced my dad to order it on Pay-Per-View.

The Naked Gun. Me and my friends went everyday to the dollar theater for about a week in a row because we were laughing so hard and missing things.

Went to see Half-baked in the smallest dumpiest theater I have ever been in ... entire experience was awesome.

Kingpin was one of the few films I can remember laughing at so hard, tears were streaming down my face.

Kingpin and the Chris Rock scene in Jay and Silent Bob Strike Back.


There's been more but those are the ones that I can remember right now.

Airplane! or Young Frankenstein

The first showing of There's Something About Mary at the hair gel scene. They didn't promote that scene at all, and had no idea that the joke was going to go where it did.

The ball punch chain reaction in Bad Santa is the hardest and longest I've ever laughed at something in the theaters.

The 'Fuck me Mr. M" scene in Election is probably second.

Wasn't the hardest, but I was the only person in a very full theater who laughed during the Tyson documentary (The scene where they show a clip of Tyson ranting at some guy and he inexplicably threatens him with,

This Is Spinal Tap

Not a new answer, but The Naked Gun & Airplane! for me as well.

<iframe width="420" height="315" src="//www.youtube.com/embed/7yc7ygB_LpM" frameborder="0" allowfullscreen></iframe>

The Ben Stiller interrogation scene in There's Something About Mary is what comes to mind.

The hardest I can ever remember laughing in a theater was during A Mighty Wind. It was during the scene when Fred Willard's character was explaining his failed tv show "Wha' Happened." I was laughing so hard I fell out of my seat onto the nasty theater floor. Fred Willard can say/do just about anything and at the very least it will make me smile.

Sheena.
Me, my brother and a friend of ours went to see it at a dollar theatre in 1984 and for some reason we were all laughing hysterically. We had not had any chemical enhancement, but I'm sure everyone there thought we were high. As far as intentional humor goes, the bar scene in Team America: World Police is the hardest I remember laughing.

Back in 1974 radio station was giving away free passes to a blind/surprise midnight sneak preview. Place was full of stoners. Blazing Saddles.

Maybe the newsstand scene in Bananas or one of several candidates in Love and Death.

Ace Ventura: When Nature Calls...scene where he is coming out of the rhino or something like that he was camo'd in. i was high and thought it was hysterical.

also, saw Dumb and Dumber for a 2nd time, high, on tv with some people. thought it was a riot!

Just Friends

Platoon

2 ones that come to mind are Dumb and Dumber. I had a hard time breathing after that because I was laughing through the entire thing. Also, Christmas Vacation, specifically the scene with the Christmas tree. My mom started laughing really hard and that caused everyone in the family to laugh with her.

Nothing has made me laugh like the scene in Fierce Creatures when John Cleese is caught in the hotel room half naked with a sheep. I literally fell out of my seat laughing. The rhino scene in Ace Ventura 2 comes close.

Planes, Trains & Automobiles and the first Naked Gun movie.