The original trope "There are no atheists in a foxhole" was created to give the impression that under times of extreme stress, all humans will look to a higher power to help them; ergo, atheism can be dismissed as human folly.
The subverted trope of the OP intends to show that using nothing but reasoning from the atheist's belief system, morality and good works do not have to be divinely inspired or derived, but can be concluded simply from the premise that there is no afterlife or higher power; that it's up to the individual, not god.
This is much more succinct than any explanation I would have come up with, thank you.
Agreed, and without expecting to gain anything from it, there is still a matter of "faith" for the atheist. Even without a higher power, you can do things in good faith, for their own merit, or, in bad faith, in order to provide personal gain, like how a still godless atheist may appeal to said higher power simply to hedge his bets. I dunno, not feeling entirely at ease with this first articulation of mine, tear it up.