Stop it man, I'm already having a nosebleed. (a comment to someone speaking in rapid fire English.)
It is also a term used by fans, regardless of their type of fandom, to express finding something exciting sexually or hot.
He quickly covered his face in an attempt to stop his nosebleed.
Girl 1: Oh my gosh, did you see the latest manga chapter?
Girl 2: Yeah, Ed looked so sexy in the chapter cover, I totally wanted to nosebleed.
2: Lucky Bastard! I could only afford nose bleed seats.