腹を立ててる

is angry

→ 腹
phrase Rare #31,615
is angry An idiom meaning to be angry with someone. てる is a casual contraction of ている.
JA: 彼は友達に腹を立ててる。
EN: He’s angry with his friend.

さぞ私に腹を立ててるだろうね?

You must be really mad at me, huh?

— フィフス・エレメント (1997)

誰に腹を立ててるの?

Who are you angry with?

カレンはね、俺に腹を立ててるんだ。

Karen’s mad at me.

トムはね、俺に腹を立ててるんだ。

Tom's mad at me, you know.

トムと私は互いに腹を立ててるんだ。

Tom and I are angry with each other.

私は先生にすごく腹を立ててるのよ

I'm really angry with my teacher.

— 8 1/2 (1963)