A mind game is her attempt of trying to get a reaction out of you, or her way of using you to get something.
Some classics are:
Your ex sleeping with your bestfriend to try and make you jealous.
Playing hard to get.
Pretending she likes you when she really doesn't simply because she likes the SATISFACTION of knowing you like her.
Trying to make her life seem perfect after a break up when it's really not. IE: Posting "I love my life" everyday on face book.
Posting pictures of herself with other guys, or purposely trying to be seen in front of you or your buddies with another guy.
Pretending she likes you to get money, a job interview, or anything else she deems as valuable.
Those are just a few. B!tches are full of tricks, if something doesn't seem right then it usually isn't. Just try and keep an eye out for certain things. If her behavior suddenly changes or you find yourself GIVING more than you're GETTING she could just be fvcking with your head. Some girls will put up being with a guy if they are continually getting something they want out of it.
