A person who has no idea of how to conduct themselves online by saying and doing things that would not be socially acceptable in real life.
Generally the actions of this person have no reflection of how they actually are.
Boy: OMG im lyk so c00l. Haunted house wif ma homes!!!111!one
Girl: I'm going too! See you there.
Boy: YESHHH! LETZ HAV S3X.
Girl: Do you have internet retardation?