why the nosebleeding ???

so i've been watching alot of anime and read a lot of manga but never in reality or movie or what ever have i seen womens body how beautiful it may be give me or another man a nosebleed so what's up with that ? sure it's funny at some tomes but i don't get where the idea came from that for example i see some girls breast sundenly i get aroused and my nose starts dripping or from what i have seen shooting blood what's up with that ps not fluent in english so sorry for the grammer errors

It stems from an old japanses wives tale about how a nosebleed was a males 'lust' leaving the body. Men (especially older men) typically get more nosebleeds then women so it became synonymous with perverted old man behavior. Also interesting is the concept of sneezing because someone is talking about you. Yet another cultural habit.