Being an asshole is contagious and makes people perform worse on many mental tasks.

Don’t assume good intentions from the other person, assume you don’t know what the other person was thinking.

Don’t assume someone’s intentions, try explain to them the effect it had on you and others.

Use humor to get your point across that the other person is being an asshole if possible.

It is better to have a hole (no one there) than an asshole. Duo lingo is very conscious about this policy. Assholes are replaceable.

Ask a reference to choose between negative descriptors that could describe the applicant, not a good and a bad one.

Performance was much better when a toxic worker was replaced by an average one than when a great worker was replaced by an average one. (By 2x)