The highest possible level of satisfaction with life only to be achieved by young white males who often go to parties, have plenty of money, and slay poon on the reg. You only know you're 'Killin' it' when you're plastered, throwin up the Shaka (surfers' hand gesture), and yelling "I'M KILLINNNN ITTTTT"
Matt: "Don't worry about me man, (shotguns a brew) I'M FUCKIN' KILLINNNN ITTTTT!"
Friend to other Friend: "Hey don't bother Matt, he's Killin' it right now.
A series of actions that puts the world's hardest workers to shame, it would look similar to Rocky Balboa as the wolf of wall street.
Luke: did you hear Dan worked 80hrs this week?
Gary: that's it?
Luke: HA! The guy also pulled off a triathalon, marathon and an Inca trail marathon this week.
Gary: jeez... that guys killin' it
12 step recovery jargon referring to someone new who talks about how great life is, now that they'resober. Usually meaning that the person is out of touch with reality.
The new guy seems pretty happy for a dude who has no job, no money and no family. He must be on a pink cloud.