I don't take it as anything more than "have a good day" and I doubt most people mean anything godly by it. Or I might take it as a wish that creation or the universe bless me ... or maybe "may you be the recipient of good vibes." One needs to think of it as the other wishing the best for another from their frame(s) of reference, and it can be received by the recipient from their frame(s) of reference.

We all have differing viewpoints. Some items are a matter of opinion, where there isn't a right or wrong. Others are a matter of verifiable fact, where there most certainly is right and wrong. In the case of whether there's a deity in the sky blessing only some people is something most on this site would see eye to eye on.

But even if you know the person you're speaking with has an ideology that is demonstrably absurd, there's not really justification to be a jerk about it. If they're offering a gesture such as "have a blessed day," so what? They're being nice. So many times throughout the day we encounter someone who says something wrong. We don't usually dedicate the time in pointing out every circumstance. How is this different?

Relevant to this discussion, Phil Plait delivers a speech covering the notion of "don't be a dick." Here's the link to it:

Thanx. I need all the blessings I can get.

Thank you, you too. Or I say Namaste.

I say something like "oh thank you, you too". It does bothers me, and makes me want to say something about it. In the end though, I know they don't really give it much thought, and are actually most of the time, just trying to be polite or whatever.

I don't respond at all. The statement means nothing to me, so I disregard it. The statement is for the speaker only, in my case. Rarely happens to me, as most people who know me, know better. as this is a small town. Just wish me a pleasant day, no blessings necessary.

When the sentiment gets Religious, I have to hold my tongue. "have a blessed day" is rather vague, but definitely religious. I would say something like "thank you" or "You too". But I'm sure my response will have some hesitation in it. Best to ignore and move on.

“Thanks, you too!” I typically do the same for “Merry Christmas”. I figure they say it because it’s meaningful to them, so in goodwill, I’ll pass it back.

Thanks, you have a good day too.

It's simply another way of saying "Have a good day." Given that, how could I be anything but polite? Just because I don't ascribe to a belief system that lends itself to such phrasing doesn't mean I can't appreciate the sentiment. My typical response is something along the lines of "And you as well."

I say thank you . I do not want to be an annoying sarcastic atheist. They are just attempting to be kind . I look at them as victims of indoctrination.Their belief has not one bit of effect on be.