In Arnold's ridiculous, but all time great movie "Commando" the final action scene has him alone in a basement with Bennett the bad guy. The bad Aussie has John (Arnold) in his pistol sight when Arnold challenges him to end their fight like men and the dialog flows:
"Come on, Bennett, throw away
that chicken-shit gun" (implying that they should end it mano-a-mano, like real men).

"You don't just want
to pull a trigger." (too clean and too quick for a guy killing a guy he hates)

"Put the knife in me
and look me in the eye...
and see what's going on
in there when you turn it. (get the satisfaction of feeling the agony of your enemy as he slowly dies)

That's what you
want to do, right?"

A moment later comes the greatest line of all time:

"Don't deprive yourself
of some pleasure.

Come on, Bennett.
Let's party." (it's the macho man's equivalent of I want you to fuck me)

So, bad boy Bennett puts the gun down and John proceeds to kill him by impaling him on a pipe spewing steam. As Bennett is dying, he looks at Arnold and as John he says "Let off some steam, Bennett."

Sick, very sick, but great phony sweat and nice camo make up.

to release built up emotion by yelling, complaining, etc

The hard hitting, immense, chainmail and leather trouser wearing bad guy off the best film that has ever been absconded onto film... Commando. People think that Arnie's quotes are funny and good, they have nothing on this bastards. Is currently letting off some steam while planning revenge on John Matrix with that double crossing bastard General Franklin Kirby

A nasty chest injury, more likely than not caused by a flying section of pipe.

To play a bass guitar or bass instrument with such abandon you would be fired from a band if you played in it. Usually to let of emotion. Much like jerking offor masturbating without the mess.

arnold fucking rules

A small, transparent and non-soundproof dome fixed on top of the Planet Express building in Futurama. Only ever seen in one scene in one episode, Professor Fansworth (supposedly) often goes in there to let off some steam. A truly pointless invention.