If you've watching a lot of internet atheists discussing God or Christianity, you've probably seen this move employed at one point or another:
"Look, I'd be more than happy to believe in God! I would change my mind immediately if the evidence were simply there. If God spelled out "I exist" with the stars in the sky, I'd believe. If a 900 foot Jesus appeared outside my window, I'd believe. If some powerful angel appeared, really seemed to be an angel, and claimed to be a messenger from God Himself, I'd believe. Supposedly God has performed miracles, and all of these would be easy for Him to accomplish, so why not do any of these if He really wants me to believe in Him?"
Now, there's a lot going wrong with this kind of claim, but I want to focus on one problem in particular: This is typically going to be a skeptic for whom, on any other related question (Christ's resurrection, healing miracles, the hard problem of consciousness, the origin of the universe, the origin of life, the origin of information, etc), they will continuously play two different cards: The "logically possible non-miraculous and/or non-intentional explanation for the issue in question" card (Christ had a twin! The universe just got lucky! We live in a multiverse and things like that happen now and then! Etc), and the "we have no answer for that now but eventually we will" card (Cosmology awaits its Darwin! Consciousness will be shown to be totally physical some day! That miracle will be explained in time! etc).
But that opens them up to the charge that, between their imagination (X happened and a lot of luck was involved!) and their delays (promissory materialism), they've placed themselves in a dogmatic position for which any contrary evidence or experience will simply be explained away. In other words, "evidence", empirical or otherwise, doesn't mean diddly to them due to their prior commitments.
Hence the reply of, "That's not true! Why, I'd be willing to believe if (listed, particular) miracles happened!"
But here's the problem: The examples of miracles given always, in principle, could be explained away in the same manner the atheist explains away any other report of miracle or evidence of God. It's not as if "luck" or "deception by a non-God agent" or "delusion" or "I don't know, but we'll have an explanation eventually" can't be deployed to explain away even the miracles the atheist says would convince him. The distinction is arbitrary - what was a God of the Gaps argument in all other cases becomes, inexplicably, a theoretically compelling argument for the same atheist.
And the inclusion of these arbitrary exceptions are supposed to serve as demonstrations that the atheist isn't dogmatic after all. Because hey, you can't be accused of dogmatism if you can name something, anything, that would change your mind, right?
Naturally, I find "I would just believe if..." claims like this to be utterly insincere. But, psychoanalyzing someone in a discussion is almost always going to be a dead end.
So, my reply to claims like this tends to be as follows: Point out that the "miracles/evidences that would make me believe" are subject to the exact same criticisms and dismissals the atheist deploys against current miracle claims or evidences for God, and thus constitute utterly arbitrary exceptions. But if an arbitrary exception to the atheistic/skeptical norm constitutes a valid and reasonable justification to believe in God, *then far and away most skeptical arguments against miracles-as-proof-of-God, natural revelation of God, and otherwise die on the spot*. If arbitrary exceptions to the norm are permissible and reasonable, then citing anything from the Miracle of the Sun to fine-tuning to the mere existence of coded language in the natural world (Perry Marshall's DNA argument) to otherwise work just as well. The only difference is that the atheist's arbitrary exception concerns miracles and evidences they don't believe have happened yet, and other people's arbitrary exceptions concerns miracles and evidences they do believe have happened.
Of course, the atheist still has some options open: Retreat into utter dogmatism (Okay, fine, no miracles or evidences could EVER compel a reasonable person to believe in God!), sacrifice the very idea of atheist apologetics (Alright, reasonable people can come to vastly different opinions on this subject, ergo theism and religious belief are not enemies of reason, ergo the evangelical atheist project is dead in the water), plea for more time (There's a response here, I'm sure of it, I just don't know what it is yet!), etc. But trying to salvage the specific, subjective preference of miracles is going to be nigh impossible while at the same time holding onto the favored skeptical moves.