The phenomenon where girls act irrationally because of indecisiveness or insecurities. Can be observed in most interpersonal relationships when a girl may act one way one day and the opposite way the next; each girl expresses her CGS differently. Though it may seem unfounded, CGS is often established because of previous relational problems (daddy issues, controlling ex-boyfriends, etc).
"Dude, why aren't you and Leslie dating yet?"
"I don't know man...she can't make up her mind about me. It's like one day she's invites me over and cuddles with me but then she ignores me for a week. I don't get it!"
"Sounds like she's got that Crazy Girl Syndrome. I wonder what caused it. You gonna keep trying?"
"Yeah. It was probably her ex. He cheated on her for months before she found out. I just gotta show her that she can trust me."