A fake smile is best used when around someone you hate. It can also be used to hide how sad you are; This definition is mostly used when in a crowded place (e.g) School, Party, A dinner, ect..
the person with this name usually lives with a facade and often hides their sadness and only shows smiles on their face. They don't like to worry their loved ones and constantly go into the emo phase.
Some short hoe: *in a jeering voice* Hey dumbass, you parked your car in the wrong spot!
Me: *instead of wasting my time explaining why I parked there, I give a fake smile and walk away*
To deliver withering insults with a faux sweet smile. It's a socialized way for high ranking classy women/men who have to refrain from stooping to their haters level when in reality, they're desperately wishing that the person would be decapitated by a flying toilet carrying their own trots and any bullshit that the looseness of their bowels cannot carry.
A fake smile can also be used to replace the middle finger or a punch to the mouth to those who don't seem to understand that you could not care less of what they think of you. Their jealousy is a good indication that you must be an awesome person of the highest calibre to spark such fury, envy and outrage.