comes from "merc" (pronounced "murk") short for mercenary.
To be killed, murdered, or otherwise mercilessly and overwhelmingly defeated or put down. (well executed and without struggle, the way a pro mercenary would do it.)
Became popular in early 2000's. Also spelled "merc", "merk", and "merked."
"He murked that quarterback! No mercy. He ain't getting up from that one."
"Did you see that fight? He murked that boy with one hit!"
"Don't even think of challenging him, man. He'll murk you before you can even reload. You got no chance."