expression, godan verb (-ku)
to cut off one's nose to spite one's face; to harm oneself by trying to harm others
Idiomatic expression meaning that an attempt to harm someone else backfires and ends up hurting oneself. The literal image is spitting toward the sky and having it fall back on you.
See also: 天に唾する
He tried to bring him down, but it was like cutting off his nose to spite his face.
そんなことをすると、天に向かって唾を吐くことになるよ。
If you do that, you'll end up harming yourself.