randomer

1) A person who does very random things either for a dare or of their own accord.

OR

2) A person who is "just there" ie doing nothing in particular.

1) Girl screaming toad repeteadly at a fat old woman who happens to be a swimming teacher.

2) Normal person: look at that guy over there he has been stood there for 3hrs. I wonder why???
Normal person 2: Oh he is just a randomer!