This is an abbreviation for the Yiddish phrase, "Kish mein tuchas" which means "Kiss my ass."
You moron; look what you did! KMT!
When a male or female has their butt on the hood of the car on a hot summer day or after the engine of the car has warmed up the hood. In most cases a male will put a girl on the hood of the car and have sex or just kiss.
Last night I put this girl on my hood of my car and had sex, she complained afterwards about her butt being hot from the engine heat, she had hot buns you could say.