Is there some wiring in the brain that prevents you from operating your bladder while simultaneously laughing hysterically? Becuase there have been a number of occasions where people I know have pissed themselves laughing.
The first time this happened was when I was visiting my cousin back when we were kids. She was wearing a leotard and I was telling her jokes before she was to run off to the bathroom. She laughed harder and harder and said “Stop making me laugh you are going to make me pee myself!” but too late, she did!
This spring a female friend and I were walking across the parking lot on the way to a PE class we had. I was telling a funny story and did not know that my friend had a full bladder at the time. She was laughing then doubled over and started screaming “oh my god oh my god etc” and said she peed her pants but I thought she was joking till she showed me- man oh man she must have unloaded a liter of pee into those shorts but amazingly used her shirt to hide it until she got to the girls locker room, where she used the hand dryers to completely elminate the evidence.
I’ve had bladder squirts from laughing, especially while pregnant.
Come to think of it, when I was pregnant, coughing, sneezing, farting, standing up etc… would cause bladder squirts.
With pregnancy, I guess it is a given that certain bodily functions are a little harder to contain, given that a fetus is pressing up against everything.
I think almost all the women I know - certainly all the women in my family - have this exact problem.
I had a boyfriend that was a kinda a jerk quite a few years ago (Like 10). One day he was ticklilng me (I’m REALLY ticklish) and I was begging him to stop. I told him I was going to wet myself if he didn’t stop.
He didn’t. I did.
He had the nerve to act surprised/grossed out.
I just pointed out that he had brougt it on himself.
I’ve borne witness to about 1,000 family dinners that feature my mom rushing to the bathroom with her hand in her crotch after someone has told a particularly funny story.
I don’t know what causes it, I do know that kegels can help it (a lot!) and I wish I didn’t do it, but hey - I drool when I sleep too - what’s a girl to do. 
I wonder if women have a worse problem with this than men do- perhaps having 9 inches of urethra is good for something after all. Heck, even if the sphincter fails, there is always the emergency ‘kink-the-hose’ until the toilet is reached.
Yeah… I do it, too. Can’t help it sometimes. Luckily, it’s not usually too noticeable.
It’s called “stress incontinence” and there’s a whole industry devoted to products relating to it, from adult diapers and pads to drugs.
Kegels do help, but as you get older and with each insult (like pregnancy) to the body, it can get worse.