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 slaypoon 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"
Friend: "How yah doin pal?"
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
A sunburn or suntan focused on the left arm. It is caused by the left side of the body being the only half that gets exposed to sunlight while driving. Presumably, it would be located on the right side of the body in countries where they drive on the left side of the road.