Some people just dig all the joy out of you.
You start deciding that you will never smile again, nor joke; that you don’t know the people around you, so you do not have to smile.
But you remember smiling and having joy is what we all crave for, and what makes life beautiful, tolerable. Even though in those moods you just think that being super serious is what will make your life tolerable out here on earth. Then you just decide to never be friendly to them ever again or smile in front of them.