idioms describing controlling anger

Keep a lid on it

To keep one’s emotions under control

“Atsuda-san might be angry, but he knows how to keep a lid on it.”

Cool, calm, and collected

Used to describe a calm, rational person

“Takiguchi-san should head the crisis management team; she will stay cool, calm, and collected no matter what happens.”

As cool as a cucumber

Calm, unperturbed

“Though everyone else was upset about the layoffs, Hori-san was as cool as a cucumber.”

Keep one’s cool

To maintain emotional control

“If we can keep our cool, we can find a way out of this predicament.”

Chill out

To relax (often used as a suggestion to someone else)

“Chill out, Sato-san. We’re stuck at this hotel until the blizzard is over so we may as well try to enjoy ourselves.”