I have heard the word 'kobe' (pronounced koh-bee) said in gaming videos by VanossGaming, usually just before he gets a throwing knife kill.
What does 'kobe' mean?
According to Urban Dictionary, "kobe" is
An exclamation, referring to talented basketball player... Kobe Bryant, used when someone does something requiring skill or great luck pretending to be skill. Created by Dave Chappelle... in an episode of Chappelle Show.
In this case, the exclamation probably refers to scoring a hit with the throwing knife.
"Kobe" is usually said when one is about to make a basket when playing basketball. It can apply to games where you might do something similar like getting a grenade or throwing knife kill, even when throwing away a piece of trash into the garbage. It comes from the legend, Kobe Bryant, who played his career with the LA Lakers. Kobe set the record for most points in a single game with, IIRC, 81 points. That's a ridiculous amount to score alone. Dave Chapelle used the phrase "Kobe" on his show which is probably where most of the 13 year old CSGO players have seen it and thought it was cool to say it without knowledge of the basketball legend or his history.