What does it mean when a guy stick his middle finger at a girl?

Well, honey, when a guy sticks his middle finger at a girl, it's not exactly a love letter. That gesture is a classic way of saying, "I'm not too thrilled with you right now." It's like a verbal "screw you" without the Words. So, unless you enjoy being on the receiving end of some not-so-nice vibes, best to steer clear of Mr. Middle Finger.