malcontent
MAL-kun-tentnounMeaning a person who is always dissatisfied and complaining
Memory hook MAL-CONTENT: never content. Grandpa Gus is never content, not even at the beach: he is a malcontent.
Even on a perfect beach day, the malcontent found something to grumble about.
In context Most of the crew liked the new schedule, but one malcontent complained about it at every meeting and refused even to try it.
Similar grumbler, complainer, grouch
From French malcontent, “ill content”: mal (badly) + content (satisfied).