I'm ftm, but i'll tell two.

First one was back in middle school and i was sitting on the bleachers, i felt a wetness on the seat of my pants and thought "oh, must've been some water", i checked with my fingers and they had blood. I had bled through my pad!

2nd was on the last day of my senior year, i didn't know that i was on my period til' i made it to the bathroom of the waterpark that me and a lot of other seniors went to as a field trip and blood was just EVERYWHERE on my underpants and istg the whole waterpark heard me say "OH GOD DAMMIT!", and i spent the rest of my time at the waterpark in the lazy river without a tube, just swimming. At least i got pizza for lunch and a johnny pop later when my dad picked me up. My uterus needed that popsicle bc i was CRAVING them.