As for the claim by the person that he/she is just being honest when they say something negative, they are often just rationalizing the fact that they were mean,or insensitive to the other person's feelings. E.g., if you say to a person "gee, you're fat", you may be telling the truth, but you're also being a dick!

I've found that most people with a need to make disparaging comments about others, don't like themselves very much . It's their burden - I leave them to it.

I learned a lot about assertiveness from a woman I dated. She could tell me anything without being offensive. It was always kind and loving. Degradation isn't honest. It's just mean.

No offense, but......Another sentence starter that makes you want to kick someone's ass before they finish what they are about to say.

The ones I’ve known were emotional abusers, or worse. My narcissist ex would say awful things; if I reacted, I was ‘being crazy’ or was ‘too sensitive’. A red flag for toxic people is to not truly apologize when told they hurt you, and refusal to take personal responsibility for their actions.

I know I don't appreciate it if it's done to me or to someone I respect, so I try to not do it to someone else. Sometimes, I've found it impossible to read the person correctly and have ended up insulting them (not on purpose), so I'm guilting. I just avoided the language.