blow one's cool
To lose your composure or self-control.
Whatever you say to the judge in court, make sure that you don't blow your cool.
He started getting confused and contradicting himself, until eventually he blew his cool and shouted at her.
Он начал запутываться и противоречить самому себе, пока, наконец, он не вышел из себя и накричал на нее.