Nosebleeding is the typical sexual expression in anime culture. Generally if someone looks at a sexy woman, his nose start to bleeding.. I do not know the origin, it needs to be researched… But the oldiest i have ever know is the Dragon Ball.. Turtle hermit sama's nosebleeding.. This pervert old-man had performed most epic nosebleedings… I tried to search hermit sama's videos but his all scenes have been deleted by privacy…

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We seeing that, almost most of anime uses this nosebleed expression..

http://canime.wordpress.com/2010/02/24/nosebleed/

Please research it!