What is I'm gonna kill it?

Typically used by band directors as a threat when you can't get a note right or scratch the floor with a timpani pedal.

I swear Jada if you don't hit that B flat I'm gonna kill you with a spoon then go after your family.

I'm gonna kill it - video

An alternative expression for "I'm tired" or "There's a little discomfort", usually used by millennials & Gen Zs.

"I'm so tired, I'm gonna kill myself"
"Oh my god I am going to kill myself"

I'm gonna kill it *dies*