What does the emoticon -_- mean?

It means the same as when someone closes their eyes and shakes their head. Depends on how it's used. If in real life, when a kid is putting macaroni in his nose, and his mother gives him the -_- face, it would probably mean, "so silly". If the kid spilled paint all over the carpet, and his mom is like -_- it would mean she is very annoyed and stressed.

its kind of like :| and T.T or --' if you know what they mean if not ill TRY and explain it... i would describe it as a face that denotes "sigh wtf? " or "sigh that wasent funny" or "omg wtf go die in a hole " ( if u watch anime its a cross between the "pissed off" red mark thing they get on there heads and the blue tear they get when they sigh or something) hope u atleast understand a lil better =]

It's an emoticon for being tired or slightly annoyed.