From Longman Dictionary of Contemporary Englishlet/blow off steamlet/blow off steamANGRYto get rid of your anger, excitement, or energy in a way that does not harm anyone by doing something active → steam
Examples from the Corpus
let/blow off steam• So kicking the cat, biting a towel or pounding a pillow aren't really much use, except for letting off steam.• Jody lets her blow off steam first.• Recess is a good chance for kids to blow off steam.• Others have behavioural problems and need to let off steam in a safe and controlled setting.• She just needed to blow off steam.• You want to let off steam?• You got upset, blew off steam.• We let off steam in graffiti, vandalism and football hooliganism.• It was recreation hour, explained Brother Andrew with a smile, and the Brothers were letting off steam. 