Although it sounds lame, I did have a pretty huge nosebleed once. And by huge, I mean huge - and the circumstances made it even worse.
So I was about 9, and was on holiday in Egypt. I was chillin' in the pool playing with an inflatable ball as you do, and the ball lightly bopped my nose. By lightly I mean it literally just stroked my nose, and it was one of those practically weightless inflatable balls.
Because logic, this caused my right nostril to suddenly spurt blood in crazy amounts. Usually this wouldn't have been that bad, but I was in a swimming pool. Blood was mixing in with the pool water, and there wasn't any tissue paper nearby to staunch the flow. Because my whole body was wet, using my arm to stop the flow didn't do much; the blood just ran down the water. I'm pretty sure the pool had to be evacuated because of all the blood.
I was hurried to a hospital in my swimshorts, leaving a trail of blood behind me. Like literally, so much fking blood was coming from my nose I couldn't even. I eventually recovered thanks to doctors giving me some sort of nasal bandage thingy that I had to wear for two days for some reason. I remember feeling ill and getting blurry vision because of how much blood I lost. It was insane.
All this because of a god-damned inflatable ball.
Thankfully the problem was addressed; nowadays my right nostril has been cauterized in a certain area (don't know the medical term) so I won't have to go through another bloodflood again. Taking out the clot after a huge nosebleed is still a really satisfying thing I somewhat miss though.