Typically a male, a tool is someone who needs a huge wake up call. They think they are God's gift to the world and will do the dumbest things to attempt to impress people, most commonly girls. Girls will laugh and this will lead this guys to believe that they are laughing because they think they are cute...but really, they are laughing because they think they are idiots. Tools also have the tendency to play with a girl's heart and not care because they think they are "hot" and can get away with anything. They may be attractive on the outside, but on the inside they are anything but.
Guy: Hey ladies, welcome to the gun show.
Girl: Wow, you're such a tool.