The Boob Tube:

Fiddledeedee: I tend to laugh at inappropriate humor. I don't intend to. It just happens. Particularly potty humor. Think "Larry the Cable Guy." Or "Ace Ventura." That kind of immature comedy. It makes me laugh until tears are flying out of my eyes.
Local Girl: The Thanksgiving episode of Friends when Rachel made the English trifle.
SocalMom: The SNL Jeopardy sketch with Darrell Hammond as Sean Connery misprouncing "An Album Cover." It's stupid, I know it's coming and it never fails to get me.

YouTube:

Mamacita: Monty Python. But that sweet video with the mother lying on her bed covered with laughing babies makes me laugh so hard I cry.
Eliza: The number one thing that makes me laugh hysterically is my kids. They can do the silliest things and no matter what they crack me up. Another thing is this baby on YouTube, when he laughs there is no stopping me I don't care how many times I've seen this little clip.

That Man of Mine:

Elizabeth from Dink(y): My husband makes fun of my anxiety attacks by singing a high-pitched "Waaaaaaaaaaaaah!!!! Waaaaaah!" as if he was Chicken Little and the sky was falling.
Elena: When my husband makes fun of my big brother, defending me from merciless teasing. I love to watch my older brother speachless on account of my honey.
Molly AtHome: "That's great." It's a line that a local politician said in the middle of a meeting where two of his colleagues were arguing with each other fiercely, and right in the middle of it all, he just said, "That's great!" in a very enthusiastic tone. He's kind of hard of hearing, and to this day, no one is sure he really knew what was going on. My husband knows just the way to say it to get me going, and then he'll repeat it until I'm almost crying.
Janet: My husband's sarcasm.

Poop is really funny. And butts. And boogers.

AmandaProbably thinking about the answer to question number two...(pun unintended, but thoroughly enjoyed)
Nettie: My 6 year old son Gibson because he loves to get out of the bath, shake his naked behind and say, "Mommy don't make me shake this patooty at you." He is PDD-NOS so the fact that he's gotten to the point where he can love to take a bath and laugh and shake his naked behind at me always make me laugh both hysterically and with great gratitude. And my laughing makes him laugh which is even more amazing!
Javajabber: I can't help but laugh uncontrollably whenever I see someone driving who is stopped at a red light or stop sign and they are picking their nose ... as though no one can see them. Uh, hello ... that's a see-through windshield you have their buddy ... not a brick wall!

Please tell us there is a blog entry about this:

Robin: I always laugh hysterically when I tell the story of my hung-over husband going to work in a machine shop wearing steel-toed boots, shiny, black spandex pants and a cropped Duran Duran t-shirt. It's a hilarious tale.

Vegas, Baby.

Missy: my brother doing his "lounge lizard" routine singing the current hits as only a true lounge lizard could
MissAnnieG: My husband doing a feminine impersonation

I was always concerned. On the inside.

Kyla: People falling. I went to a very small college in northern Wisconsin. It snowed, a lot, in September and October and November and December and January and Febru...you get the idea. There was very little to do, most often we could all be found in the dorm, all 800 of us drinking and smoking and watching people fall. Right outside the big picture window was a hill, the only hill on campus with the only sidewalk on campus which lead to the only other building on campus. Everyone had to walk it, everyone fell, everyone! It may not sound funny, but imagine yourself 6 beers into a twelve pack, wearing an illegal smile watching not one person fall, but dozens one right after teh other. They all know they're being watched, they are all trying with everything they have to stay upright and...there goes another one. The best times of my life happened in front of that window.

Hey, I got one for you!

Still Standing: Trying to tell a simple joke. Nothing really, just a dumb little joke that kids tell, but I can NEVER make it through the entire joke without falling out of my chair. I'm not even sure that anyone else thinks it's even funny. They are too busy laughing at me rolling around on the floor with tears in my eyes gasping for air. Now I know that you are dieing to hear the joke. . . .wait for it. . .A three legged dog walks into a ... (heeeheee) . . .walks into a bar. . (hooohoooheee hee ...hee sniff) and he says (HAAA HAAAA!! HAAAA!!) I'm lookin' for the man who shot my Paw. (unable to see by now, children are asking if I am okay) It gets me every time!
Rachel: Jokes - the sillier the better. Knock Knock who's there? Interrupting cow Interuppting cow ...MOOOOO!!!! And then my kids made up one about my (very, very clean, OCD-clean) brother: Knock Knock Who's there? Interrupting Uncle Alec! Interrupting Uncle Alec ... Be Clean! There are so many wonderful permutations of this joke!
Margalit: Playing XBox games with my son. I'm old, people, old. I do not have the hand eye coordination I used to when I was a young sprout. I lose at every single game. I have no aim. I can't remember which buttons do what. I crash my cars constantly. When snowboarding I go off the hills. I can't find the other players in bumpercars. I'm terrible pathetic but it's so funny I laugh until I cry.

Nonsense - this is what we have children for, right?

Tricia: Well, although perhaps slightly bad mannered, it cracks me up every time to witness my children walk into walls or trip over their own feet!
clickmom: My 13 year old son can bring me to my knees any day of the year.

Kid Humor

Tessa Lemmons: My son giggling and laughing helplessly and without reserve or our Long Haired Dachound errr... molesting a character pillow... (Stoopid dog is a girl btw heh)
Jessica Knight: When my 4ry old calls me Sugar Booger.
Karen Rani: My kids make me laugh hysterically all the time. Just yesterday, I asked Thomas to bring me his cup and he put his hands on his hips and said, "Mooooommy! You're making me SICK!"

Bong, bong, bong. A recipe for laughter.

Erika: I can't think of one thing that makes me laugh hysterically every time, but I can remember one incident many years ago that I laughed hysterically about. My mom and I were watching Weekend at Bernie's, and while not the greatest movie, there is one part that's pretty funny. When the two guys are driving the boat, and Bernie gets tied up in the ski line and is being pulled along behind them. He begins running into the guide poles, "bong, bong, bong" My mom and I started giggling, then we were rolling on the floor. We still talk about it sometimes.

Vicious, but funny.

Jack's Raging Mommy: Snorting- Every time I snort when laughing I just collapse into hysterical laughter and usually end up snorting several more times- it's a vicious cycle.

Amen.

Busy Mom: The movie "Airplane"
Mamma: My best friend channeling a Solid Gold dancer--dead sober--in the middle of a crowded bar.