A phrase coined and popularized by the band thrash metal band Lich King. Something you yell in a mosh pit,(usually at a metal show) when you want to kick a poser's ass, or get other people to help you take down someone being a bully in the pit.
Hate mosh is the most violent form of hardcore dancing. Started in Jacksonville, Florida; by crews like MTS and OPDS, hate mosh is similar to hardcore dancing, except you don't do it inside of a mosh pit, you do it against the people who aren't dancing.
Hate moshers usually run and jump into a crowd of people watching the show and throw punches and kicks.