Top Definition
A fake friend who secretly wishes you to fail at everything.
Since my friend Jon secretly wanted me to get my ass beat in a fight, he was being a sideline hater.
by Night_Nite May 26, 2014
Someone who uses you and likes to see you fail in life, school, or even your job. A big prick, honestly. He maybe uses you to see your information or something that you own such as a game, car, or maybe even your own house. He in the end reveals he is your hater. You then succeed in kicking the prick in the nose and breaking a bone.
Dang, Manuel's best friend is a sideline hater, that's just a shame

Josh used to be friends with Garrett until he found out Garrett was a sideline hater using him for money, fame, and games. That's super lame.
by Ultraf0xDictionary June 05, 2014

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