An insult formed by removing the word "jack" from jackass and replacing it with the word "jerk." Basically describes a person who is being a real jerk. Used when you need to get the point across that a person is a jerk where just the word jerk won't cut it.
"Don't be a jerkass."
"You're such a jerkass, this is why nobody likes you."
"Fuck you jerkass!"