To take part in a perceived fun activity or activities after an intense emotional taxing day or days at work , school, or home. Always associated with doing something different to get your mind away from your problems. Typical non-harmful activities include exercising, sex, playing games, camping, dancing, watching a movie, listening to music.
Some activities can be satisfying but ultimately detrimental to your health such as binging on alcohol, drugs, smoking, or food.
Other activities can be criminal. Spray Painting walls, vandalizing homes or places of businesses, rioting (usually after a favorite team loses), or physically taking their aggressions out on people (spousal abuse, worker abuse or detainee abuse have been cited as blowing off some steam).
Buddy 1: "Damn, your boss is making you work weekends and overtime over something he did wrong? WTF
Buddy 2: "I know man, well lets go to the bar, grab some brews and blow off some steam"
Example 2 (CBS News):
Rush Limbaugh trying to explain why detainees were tortured by U.S. personnel in Abu Ghraib, Iraq:
"This is no different than what happens at the Skull and Bones initiation, and we're going to ruin people's lives over it, and we're going to hamper our military effort, and then we are going to really hammer them because they had a good time. You know, these people are being fired at every day. I'm talking about people having a good time, these people, you ever heard of emotional release? You ever heard of need to blow some steam off?"
Her: "I don't feel like having sex tonight, my hair is a mess and I have a headache....(10 seconds later) ..Where are you going?"
Him: "Gonna blow off some steam (Drives off)"