Insults, put-downs and epithets are always inappropriate, but they are still used. This is disrespectful and commonly used by narcissistic personalities as a result of a high sense of entitlement: you do not matter, so name calling is fine.
“You are not much of a negotiator.” “You are a misogynist.” “You are stupid, a cad and a boor.” “Are you new to this job?”
Disregard name calling at first. If it persists, know that the opponent is incapable of a higher thought method of negotiation. Call them on it.