Why does this guy try to hide his smile towards me?

[Anonymous]

So me and this guy are quite close friends, whenever he used to look at me he used to pull quite a blank face.
But lately nearly every time he looks at me he smiles or tries to hide the fact he is smiling.
Why is he smiling all of a sudden? Also why does he sometimes try to hide that he is smiling at me?

[new_girl22]

Well honestly he could like you but is shy to show it

[QueenJ]

maybe it's something about his teeth?

[Anonymous]

Is he related to the Joker?