Describing a super funny situation or occurrence. Often used by airheads or valley girls in cliques. Occasionally used by ghettofied bourgeoisie or people too lazy and dumb to pronounce the full word "hilarious".
My sister came up with this word to describe me when she was about eight years old. It is a portmanteau combining "hilarious" and "comedian." It is used sarcastically conveying the idea that "although you think you're funny, you're not."
Dude: Jack be not nimble; Jack be not quick; Jack couldn't jump over that therecandlestick.
Bro: Hilarious, dude.
Dude: I'm a poet, I knows it.
Bro: Yeah, you're a real hilarian.