Let off steam
Definition 1 of 1
Pro Tip 1/3Emotional Relief
Used when someone needs to express strong emotions or relieve stress. 
He was so tense, he really needed to let off steam, so he went for a run.
Pro Tip 2/3Casual Expression
It's often used in casual, informal conversations rather than formal settings. 
After exams, we need to let off steam and just hang out.
Pro Tip 3/3Physical Activity
Commonly associated with doing something active or vigorous to manage stress. 
I'm going to the gym to let off steam after that argument.