A Fake Smile
A fake smile is what you wear when you see someone you hate, like a fat loser, a cheating ex, or a guy who thinks he's a gangster.
I smiled at my ex when she showed up at my birthday party. I was thinking about how I wanted to throw her in a lake.
My neighbor smiled at me when I told him I was going to beat him up. He was thinking about how he wanted to run away and hide in a closet.
My cousin smiled at me when I told her I was going to steal her boyfriend. She was thinking about how she wanted to punch me in the face.