. . . that it made you seriously question who you are?
What I laugh at generally confirms who I am.
Same. I’m sometimes surprised at the strength with which certain things hit my funny bone, but never that they hit it in the first place.
And just to validate the OP, yes, the Pooh meme generally makes me chuckle.
I laugh my ass off at news videos of cars sliding into each other on icy roads, so I’m hopeless as a human.
Honestly, if you’d asked me whether I’d find something like that funny, I’d have said “Eww, no way.” Just not my thing, never been a fan of slapstick.
Just now I re-opened it to try and take a critical look, but was again instantly reduced to a wheezing, weeping, full body seizure of laughter, gasping for breath.
I just have no idea.
:o 
The “Taranshula” scene from Red Dwarf (go to the 56 second mark if you want to skip the preamble) has sent me into paroxysms of laughter like nothing else I’ve ever known. Loud, uncontrollable, breath-stealing, tear-making, bladder-straining laughter.
It has stricken me this way several times. Even now it still gives me a good chuckle. Something about the way Lister and Cat describe what’s going on offscreen while typing on the computer just puts my funny bone in overdrive.
I sure many of you who see this scene will think, “Meh,” at most. All I can say in defense is that funny bones are weird.
There was an incident several years ago where a woman had a pet chimpanzee and at some point the chimp acted aggressively and basically ripped the woman’s face off (I am like 90% sure she lived but was badly hurt). The 911 call from her friend screaming about the Chimpanzee was an early case of something going viral (I remember Howard Stern played it at least once). I will state that I know there was nothing funny about what happened and if it happened to me or someone I knew I would be horrified but damned if the audio of the call didn’t make me laugh my ass off every time I heard it.
** Did you ever laugh so hard at something . . .
. . . that it made you seriously question who you are? **
Yes, but I’m sure it had something to do with the mushrooms.
I’m sorry, but as a male, cartoons and jokes of this specific type are not funny. And it is entirely because I have been subjected to this event. It is not pleasant. I suspect that most men cringe at the very thought of being kicked in the genitals. And that’s from day-to-day life experience. Fiction authors and filmmakers have got this right: it completely incapacitates the victim and is painful for a long time. I’ve been a victim. It’s not a joke to us.
My son and I were driving home from the Mayo Clinic where he had a week of horrible tests. We drove past a billboard that was advertising an appliance store. My son read it out loud. He said, “stainless steel refrigerators, only $1500”. That was it, nothing funny there, but I just kind of giggled, then he laughed, then I laughed. Pretty soon we were laughing uncontrollably. We’d stop for a few seconds and then one of us would start up again causing the other to start. We had tears streaming down our faces we were laughing so hard. We must have laughed for at least 15 minutes straight. I’m sure it had a lot to do with all of the stress and anxiety we were feeling. But it sure felt good to laugh like that.
Please move the Deer Crossing Signs
And if you really want to question reality - watch the tv show Happy!.
I love MTV’s “Ridiculousness” (hosted by Rob Dyrdek). It’s a video clip show of people doing dumb stuff; I’m fairly certain that a few folks died in the clips died I watched “America’s Funniest Home Videos” for a long time until it turned into glurge like surprise marriage proposals and babies going “ga ga ga ga.”
In short, I’m really a 15yo boy.
Is there a man alive who hasn’t taken a shot to the grapes? I’ve certainly taken my share. It hurts plenty. And it’s also funny, in a way that spraining your ankle or breaking your arm isn’t. I don’t know why, but it is.
The viewing audience for America’s Funniest Home Videos would appear to agree with me on this, as testicular impact videos appear on pretty much every episode.
The OP’s cartoon leverages that humor by unexpectedly superimposing it on a pair of beloved cartoon characters to whom you would never think to attribute such explicit anatomy, language, or behavior.
That is a surprisingly good show. 
I don’t know why it hit me so hard, but the first time I saw this, I laughed for about half an hour.
I think I mentioned this episode in another thread.
Once upon a time, Mrs. J. and I used to get our taxes done at a (H&R Block?) kiosk set up in the local Sears store. One year, our preparer was a solemn, 70-ish, impeccably tailored Indian gentleman named C.U. Mehta.
It was probably a combination of repressed hilarity about his name, plus the unending manner in which he painstakingly explored every possible angle which did not apply to our situation, but we finally got the giggles about the nth time he prolonged the session with another non sequitur, which led to outright helpless laughter (punctuated by indignant looks from C.U. Mehta), during which I finally had to get up and out of there before I coughed up a body part.
It didn’t make me question who I am, but for awhile I seriously questioned if it was safe for me to be out in public. 
I don’t know of any that made me question who I am, but of all the myraid Peanuts cartoons I have been exposed to in my near-65 years (which means a lot), this one has stuck with me and can still make me grin, if not laugh out loud. Why? Can’t really say, but like Hopeful Crow above says, funny bones are weird.
https://pics.me.me/peanuts-though-her-husband-ve-solved-our-problem-he-said-21420830.png
The hardest I can recall laughing was at a Far Side comic. It’s in the complete collection; I’ll try to get a page number later.
What it is, basically, is a panel of grassy hills, a nice pastoral morning scene, with a tree in the foreground. A monkey-like creature has clearly just fallen from the tree and smacked into the ground, with a surprised look on its face.
The caption says, “The Dawn of Man.”
Every time I look at that thing, I crack up, sometimes until I can’t breathe. My father-in-law too. Our spouses, though, just look at us funny.
Oh, good, this saves me from starting a separate thread tentatively titled “I Guess I’m Weird Then!”. There was this pastry chef on Chopped who was talking about his sourdough starter, who “lives in his bucket under the sink. His name is Carl and he has his own nametag. After a year, I put a bowtie on him to celebrate his birthday.”
I thought this was adorable. I would totally name my starter, who would be around for years and play a big role (roll?) in my bakery. Ted Allen says “You’re weird, aren’t you?” “Yeah, but it’s fun!” Count me in, Chopped guest pastry chef!
I have found a few people in my life that are triggers like this.
The right joke sends us into a giggling feedback loop