let off steam

let off (some) steam and blow off (some) steam 

1. Lit. [for something] to release steam. The locomotive let off some steam after it came to a halt. With a great hiss, it let off steam and frightened the children.

2. Fig. to work or play off excess energy. Those boys need to get out and let off some steam. Go out and let off steam!

3. Fig. to release one's pent-up emotions, such as anger, usually verbally. I'm sorry I yelled at you. I guess I needed to let off some steam. She's not that mad. She's just letting off steam.

See also: let, steam

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let off steam  (British, American & Australian) also blow off steam (American & Australian)

to do or say something that helps you to get rid of strong feelings or energy Meetings give people the chance to let off steam if something has been bothering them for a long time. After a long journey, the kids need to run around a bit and let off steam. I've told her she can call me and talk any time she wants to blow off steam.

See also: let, steam