Why do people who do not belive in G-d care if I pray for them ?

Well really that depends on why you are praying for me. Is it because I am an atheist (not really but...) and you are praying to save my soul then yes it would offend me that you cannot just accept that I choose to believe something different then you. Do you pray for your muslim friends or pagan/wiccan friends because they believe differently?

If it is because my family is going through a rough time then that is different because you are simply telling me you are thinking about us and hoping we make it through it. That is not a problem for me and I tell friends and family that they are in my thoughts all the time when they are going through rough times.

Is it that hard for you, OP to respect someone's wishes? Pray to your heart's content, but if someone has asked you not to pray for them and you do it anyway and THEN tell them about then you're just being an asshole.

To me as an atheist, it's the equivalent of saying "I'm going to do absolutely nothing for you." when someone says they are or are going to pray for me. Prayer is the other person PRETENDING to do something to help when they are, in reality, doing nothing that will help or change the situation.

Probably because you are being condescending.

I don't need prayers. I work things out for myself. I deffinatly do not need salvation and honestly that's probably the only thing that I find offensive, for a person to know my beliefs and yet still tell me how they pray for god to work and change me. It's not really the prayer that's offensive it's the mentality of the person.

Maybe these will help you understand:

Would you be offended if I as a witch said I preformed a spell on your behalf?

Because I see it as arrogant to even consider doing it, let alone informing me of you intent to do so. By doing that, you are stating that you do not respect my wishes or my beliefs, and therefore have only your own selfish desires in mind when praying for me, you are really not considering my own well being.

Besides, in some religions it's not only rude or disrespectful to pray for someone else to a god they don't associate themselves with, it can actually be considered harmful. In other words, if they believe in another god(s), then you might just be doing more harm to them than good. It's the refusal to understand such concepts that pisses people off.

Maybe because they usually get the "I'll pray for you" in a demeaning, holier-than-thou way, as in "you're so lost, I'll pray you find G-d" or something like that. I'd probably be pissed too if someone used something that's supposed to be selfless and positive to demean my beliefs.

I find it compassionate when my Christian friends pray for me. They feel helpless and need to do something. That is what their faith and beliefs say that they do in that situation. I don't want to be judged on where my life path has led me to my beliefs and I won't judge others for it either. If you feel like you need to pray for me, pray on! :)