Cynic

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A cynic is a headmate that thinks very negatively, like a worrier, but wants to disrupt life in some way for other system members or the system as a whole.

They may do this because they want other system members to understand or relate to their constant negative emotions or because they have some anger issues or because of a number of other reasons.

Their disruptiveness can be "small" things or things that are bigger. It all depends on how disruptive to life they want to be and how disruptive they're allowed to be.