I was 17 going on 18 and it was the last year of Senior High school. By some dumb state law the school had to show some historic movies during an assembly about once a month.
This one was Victory AT Sea. Ok so we all file in and im in the middle of the row of classmates. The movie starts, music and ships and bombs and water,water,everywhere. Soon I had the feeling my bladder was filling for no reason. I started to really have to pee. The movie drones on and my piss urge is getting worse. My bladder is throbbing and I have this intense irritation of some sort. I was like, if the guys can relate to this,almost like Im going to cum in my pants. The feeling gets worse and Im thinking of getting up and leaving, Id have to make a whole row of mates to get up as I squeeze be with a teacher on then end of the row.
Im getting to the point I feel Im going to piss my pants, like in 12th grade, after all those years Ive seen some of my classmates piss themselves, now its my turn. This is going to be really horrible. Im getting up nerve to get up and leave with my pee right at the end of my penis. Im like holding my dick in my hand thru my pants pocket.
I feel a little squirt leak into my briefs. I shut it off.
Im ready to flood my pants.
Then, suddenly the movie screen goes black, it stops!
The film broke! The lights come on and im holding on for dear life so I dont piss myself. The principal goes to the front and says, "bulb went out in the projector and we cant fix it".
So then every one gets up to file out. Lucky too, the seniors were always the last to come in and the first to leave. We filed out the auditorium to the hall and sorta broke up to go home for lunch or whatever. I headed for the boys room and just barely made it. I took out my dik and pissed for about 2 mintutes-hot pee.
Then I went on home for lunch really afraid to come back to school.
I got back after and we had our first class and my pee urge came back. But it took the whole 45 minutes for it to get bad and the bell rings. I head for the boys room and piss again hot pee.
The next class the same until the end of day.
The next day I took off school and stayed home with a "bad headache".
I finally realized it was a sort of a cold or UTI in my bladder.
I had one of those again about a year ago, woke up with it, and hand pissed my pants in bed.
I got some medication this time and its been ok since.

But almost pissing your pants in school, ya, its scary..