A Hategasm is an explosive and immensely satisfying release of anger that usually arises when observing someone truly vile either horribly maimed, injured, or killed, often in dramatic fashion. Revenge movies are often geared towards the climax towards the righteous hategasm, at which point babies are often the victims of violence.
Bro A: "Yo guy, did you watch that episode of 24 last night?"
Bro B: "FUCK yes, I can't believe he finally killed that Miranda bitch, I was praying for her to die for the last 6 weeks"
Bro A: "Holy shit, but when he did, I hategasmed so hard I punched a baby"