I’ve probably watched this a dozen times and it still cracks me up. Lost Baggage.
I do not happen to watch many English sitcoms, so I guess I miss out on some great comic entertainment. But I have watched The Big Bang Theory. I remember I laughed out hard at thisscene.
Sheldon : “I need soup”
Howard in his mother’s voice : "Then call your own mothah!"
hehehe
Other than the boatmurdered dwarf fortress saga, the thing that made me laugh the hardest on the internet was this pic.
The Christmas episode of “It’s Always Sunny in Philadelphia” from a couple of years ago features a naked Danny Devito hiding inside a leather sofa (to spy on the guests at a party), but he gets too hot or can’t breathe or something and has to burrow out of the sofa.
I laughed so hard and for so long my wife thought I was having a medical event. I rewinded it and watched it again and it was just as funny the second time.
May not be to everyone’s taste, but the hardest I can remember laughing in a theater was at the naked hotel room fight scene in Borat.
Bill Cosby in concert, about 1978 or so. He came to my college for Mother’s Weekend, and Mom and I went to see him. Mom was laughing so hard I thought she’d have a heart attack. 
In an episode of The Golden Girls, Rose plans a surprise for Dorothy at a Chuck E Cheese type of place.
Oops - forgot my all time favorite - on the Roseanne Show, Jackie has to make a phone call to announce dad died. This scene that had me laughing so hard I couldn’t breathe…
Oh, I remembered! It’s something a Doper linked to a few years ago, and every time I think about it I still giggle. Then it was mentioned on NPR yesterday with an excerpt or two, and I started cracking up in the car.
Reverend Jim’s Driving Test, from Taxi.
Slow down!
George Carlin’s Seven Dirty Words (audio obviously not safe for work due to language). I’ve probably heard it at least a dozen times if not more by now, but it kills me every time.
I am searching Czarcasm, I know I didn’t make it up. He’s a Hispanic migrant worker. I’m trying to remember which show this skit was done on, because I know he had a partner, but I can’t picture him in my mind. I’ll keep digging and post a link once I find it.
While elephant story is probably my all time favorite, I can’t keep a straight face for the SNL skit, Colonel Angus.
Chris Rock - How to Not Get Your Ass Kicked by the Police
Well, it’s hard to have a definite #1. What I think I laughed at hardest most recently was pregnant Amy Poehler doing the Palin Rap on SNL. Something about the combination of the bobbing babybelly and the hands doing gangsta guns shooting moose…
For one-panel cartoons, it’s hard to beat the stuff in theNew Yorker.
Except maybe for the old National Lampoon.
The hardest I’ve laughed in at least the past ten years was at ladder goat
A few of us are fond of this 1980’s standup routine by by Bob Nelson. It isn’t completely PC but I thought it was hysterical when I first saw it.
Text and pictures (not video)
Return to the science fair.
Because if you can’t laugh at kids trying to do science, then you’ve lost the joy of living. And there are a lot of… …you know what, I can’t do this, I’m heading back over to the fucking in space experiment.
Tim Conway in The Dentist.
Dad at The Comedy Barn (about 1:30 in).
This Tundra comic (the big one on the right):
