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!
The ones nobody invited to the party, but who hang around anyway - no-one will ask them to leave, as no-one knows who invited them in the first place.
You: What's up.
Randomer: Hey, not much, you?
You: Nice, not much.
Randomer: Cool, later.
*You both leave the lockers and forget about each others' existence*
Sane Person : Stfu, you complete & utter idiot.