The term 'curmudgeon' has a negative tone and suggests unpleasant behavior. He was the curmudgeon of the office, always complaining about something.
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Older Characters
Often used to describe older people, implying stubbornness or a set-in-their-ways attitude. My grandfather, the family curmudgeon, refuses to use a smartphone.
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Not Always Literal
'Curmudgeon' can be used humorously or affectionately for someone who's only occasionally grumpy. Uncle Joe is being the holiday curmudgeon, avoiding the festive cheer.