The easiest and most frequently done thing by everyone is probably just to clench their fists. Without exception as well as myself, I clench my hands when the moment of anger is unstoppable but cannot be released for many reasons which is better than venting your own anger.

Image by wendy CORNIQUET from Pixabay
Indeed, it seems that the meaning is very suffocating when we clench our hands when anger rises. Which means that something very undesirable happened.
Without sorting out an incident that happened, when someone does something like clenc they hands it could mean something other than anger of course. But just a basic mapping of the condition of a person clenching his fists might be said when it happens is when anger comes.
Like fighters or boxers who are used to clenching their hands, this is how situations where clenching occurs is more common.
Clench my hands, can also be done upon request from a condition when I ask a third person to make a fist. Conditions may be when having fun or having fun with loved ones.
So basically various things can really happen when discussing the sentence from clench my hands. Whether it's positive or negative, everything can happen even if it's only in the smallest conditions that are usually done by every human being.
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