I have been known to reply 'Good luck with that' which earns me a baffled look and makes me chuckle.

Depends upon who is saying it. There was a mentally challenged woman at a local fast food place that would run food out to cars. She always said have a blessed day. Didn’t bother me in the slightest because I knew she was just being nice and most likely didn’t have the mental capacity to critically think about religion.

Older/elderly people I usually let it slide.

Very occasionally I’ll say thanks but I’m not religious. If someone knows I’m atheist and is trying to get a rise out of me, I’ll tell them that they can pray but I prefer to think

Depends on the context. If they are saying it as a way of "saving" me from my pagan ways, I point out that it's a waste of time. If they are saying it as a way of giving me comfort during some bad times, I simply smile, nod and move on. But I usually get it in the former and not the latter, so I'm usually telling someone to save it for someone who cares.

It depends on circumstances but usually it is "please don't."

g

Me too I say, "Thank you. Appreciate it. I'll put in a good word for you too."

As agnostic I just say thanks and move on...

I respond with, “oh, well, I’m atheist, but ok.” If they are saying it in response to finding out I’m atheist, then I respond with something matching their level of rudeness

I run into the problem with - god bless you, when i or someone sneezes.
i am not saying it, and i cannot thank them for it if i do not believe.
it gets so that when i sneeze or someone else does,
i wanna run away from the situation.
people get offended if you do not bless them after a sneeze
or if you do not say thanks after you sneeze and they bless you.
even when i did believe i thought
why waste a blessing on a sneeze?
manners? says who?
if someone is choking on something,
now there is a time for a blessing, not a sneeze. :\

I say, It is not helping you must make a better effort.

I take it as their way of appreciation/concern. It's not very useful, but I'm not one to ask for things from people so I can't really complain about what I do receive.

"Thanks. I'll be thinking well of you, too."
Fini.

I'd ask them which god they will pray to, and then when they respond, tell them, "OK, I will pray to Satan for you too." That's my smart ass remark for the day!

I simply thank the person as it's a way to wish you well. Why take it in a negative way? Just because we don't believe in the same thing?

Not an atheist and think that if it is meant benignly it is a lovely thought. If it is in a condescending manner just shows ignorance.

Nothing to get upset about.

Depends on who says it and where I am.
-If I'm at work and a co-worker says it: "Why?" and/or "No, thanks."
-If I'm at work and a client says it: "Oh...umm, ok."
-If I'm out in public and a stranger says it: I'll laugh and walk away
-If I'm out in public and someone I know says it: I'll give them a "WTF?" look (because most likely they know I'm an atheist and that would be weird if they said that), say "Why?" but with an attitude like I'm pissed off

A little off topic, but it gives me a chuckle and a chuckle goes a long way for me these days.

Last year my wife and I were invited out to dinner by my female cousin along with about ten others. My uncle (her father) who was 90 at the time was the patriarch of the family and present at the dinner. He has never been religious, but my cousin had converted some years past. Dinner was served and my cousin asked her husband to pray for the food. We all bowed our heads (sans me and my uncle) and my uncle said (picture a 90 year old grumpy man - like Walter Matthau in “Grumpy Old Men) “What the hell is happening?” My cousin says we are going to pray. “What the hell for?” That was it for me. I had a full release of laughter that would not, could not be stifled. Will never forget it.

"Thank you. I'm going to a party of cavorting druids and dung for dinner in your honour later."

I’ve only had it a few times...but a simple thank you is all I think I responded with. Why be ungracious, especially if it’s said sincerely.

"That won't work," I reply merrily.

Thanks, and I will think for you.

The same way I respond when people say "bless you" after I sneeze: "Thank you."

"thanks ... we can all use all the help we can get"

Thanks. I'll take all the good luck I can get. Do you carry a rabbit's foot?

"I wish you wouldn't, unless you think you would like for me to sacrifice a small animal for you?"