Replying to Girls...arghh

I cant figure them out! Ok tonight I was making with this girl at his party. After 20 minutes we stop for a second (everything is fine)and she talks to one of her friends. When I come back from the bathroom she is just crying and swearing at me. I dont know why. I cant figure out girls. Now she is just pissed off at me and I have no clue why, and she wont tell me either. Why couldn't god let us guys know what goes on in their minds?
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Andrew

'...And sometimes I park, in handicapped spaces,
While handicapped people, make handicapped faces'
-I'm an Asshole by Dennis Leary