probably because he's of the age when guys *mean* to say, "hello. i think you're awfully cute, and i would like to get to know you better," but the closer they get to the girl, the more their brain stretches itself out, ties itself into a firm knot and ceases to function on any reasonable level. because when he gets close to her, there's an electrical storm running around in there and none of the parts of his brain are talking to any other parts of his brain. so he winds up acting like a goof and, once he's out of the sphere of influence, he feels like an absolute idiot, which only guarantees that, the *next* time he tries to talk to her, it'll all happen again, only louder.
guys really have a hard time of it.
(the female version of this generally manifests as the giggles, which become more intense as the object of desire comes nearer.)

