How to respond to "God bless you" statements

[Bob Kelso]

I always retain a certain modicum of respect for those I don't know and I say "thanks" or "goodbye" or something equally innocuous.

If I know the person and they know I'm an atheist, I generally reply with "No thanks" if it was said offhand, but if it's intentionally supposed to piss me off I'll reply with a "Fener fend*" or "May the Force be with you".

*My uncle is a fundie who has read Malazan Book of the Fallen as well, so this reply is mostly for him since he understands it. Fener was one of the gods of war in the series and this was a common statement throughout the series to ward off evil or unwanted circumstances.