The boiling point of a liquid is the temperature at which it becomes a gas.

The boiling point of water is 100°C. 水的沸点是100摄氏度。

the point when a situation is about to get out of control and become violent

UK The situation in the inner city was reaching/at boiling point, so the police were out in force. 内城的形势快要失控了，所以警察都全副武装出动了。

US The situation in the inner city was reaching/at the boiling point, so the police were out in force. 内城的形势快要失控了，所以警察都全副武装出动了。

the stage at which someone is about to become very angry