Why are fangirls so crazy while fan boys aren't?

Whenever there's a Justin bieber concert or so on the walls end up covered in blood and many girl go to jail and the hospital because they decided to pick fights with other girls claiming to own the guy. Fanboys on the other hand retain their sanity. Why are fangirls slaves to their own lust while fanboys keep it straight?
Why are fangirls so crazy while fan boys aren't?
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