The word bless is used variously depending upon the situation.
1.Bless is commonly used when somebody sneezes because apparently when a person sneezes their soul is trying to escape their body (which is obviously a load of bullshit) Saying "bless you" when somebody sneezes is just a mark of politeness, more like having manners.
2.In England "bless" is genuinely often used instead of saying "aww" This often confuses a lot of my American friends.
3. Again in England "bless" is also used sarcastically in a patronising manner. Some may find this funny or annoying, depending upon their humor but sometimes the phrase "Bless your cotton socks" is over used which makes people punchable.
Sarah: "Bless you!"
Mark: "Thank you :)"
Samantha: "Look at this sweet message Daniel sent me!"
Lorraine: "Ugh I fell down the stairs this morning and now my back really hurts"
Hannah: "AHA bless your cotton socks."
Lorraine: "Mhmm, I think Peter is meeting me after school today"
Hannah: "Bless his cotton socks."