The idiom "grind one's teeth" means to clench or rub your teeth together tightly, usually as a sign of anger, frustration, or anxiety. It is a physical expression of strong negative emotions.
For example, if someone is very angry or frustrated, they might grind their teeth together as a way to cope with their emotions. It can also be a sign of stress or anxiety, as some people may unconsciously grind their teeth while they sleep.
You can use this idiom in a sentence like this: "Whenever he thinks about his ex-girlfriend, he grinds his teeth in anger." Or, "The thought of the upcoming exam made her grind her teeth in anxiety."
Overall, "grind one's teeth" is a common idiom used to describe a physical manifestation of negative emotions, particularly anger, frustration, and anxiety.
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