I found a PureWow article (“How to Deal with Toxic Coworkers, According to a CEO”) that shares the thinking of Mason Farmani, a fractional CEO and conflict mediator. Below is a summary of the key points & tips — happy to also pull up the full transcript if you want more depth.

Before acting, it helps to see what you're dealing with. Some warning signs Farmani points out:

Chronic negativity: when someone is always pessimistic, complaining, and bringing down morale. PureWow

Gossiping: spreading rumors, sharing others’ personal or confidential info. PureWow

Inflexibility: refusal or aversion to new methods, resisting change even when needed. PureWow

Overly competitive vs collaborative: when a person treats coworkers more as competitors instead of collaborators.