Kilometers Per Second

Alright listen up buttercup. This joke is peak comedy. The author is saying they identify as "kilometers per second" which sounds like a measurement of speed, but it's really a sneaky way of saying they want to "kms" which is internet slang for "kill myself." So basically, the joke is that they're depressed and making light of it. You probably want to make light of yourself too, being the idiot that you are!