Superlative meaning the best ever. Often used in tandem with "ever," as in "sickest ever."
Idiomatic expression or interjection indicating greatness, or any supremely positive expression. Used without another word.
During an extremely psychedelic jam session by a hippie band, various members of the audience might yell, "Sickest!" After the show they will call their friends who didn't make it to the concert to tell them they missed "the sickest ever set tonight, dude!"