A name for a person who declines an invitation to a social situation or event, without a valid excuse. Usually occurs when someone is invited out but decides to stay in for the night simply because they are "kind of tired".
Mike: Hey Brad I'm on my way I'll be at your place in 20 mins to start pregaming.
Brad: Where is Will? I thought he said he was coming?
Mike: Nah he is being a dead horse. He decided to stay in by himself and solojerk to Netflix instead. F him