I often don't say bless you to people who sneeze. I will if it was someone I know or something, but not always. I find it strange that someone can get upset if you don't say it. Why are you owed that? It is not as if you did something special?? I know the origins of bless you.
I most often say bless you to my boyfriend when he farts, cos I think it is funny! Other than that, only if I feel like it.