An attitude of enforced congeniality with someone you cannot stand which is very very subtly detectable by the other person, but not proveable.
1)There's the boss - quick, pretend she's not the manipulative control freak that you would fire if the roles were reversed. You must show her your Nice-Hate smile in order keep your job so you won't starve. She will no doubt Nice-Hate smile back at you.
2) Oh no my boyfriend wants me to go to a party and his ex-girlfriend will be there. I will have to go into Nice-Hate mode. "Oh hello dahling! Fancy seeing you here -how are you? Mwah mwah."