Captain America standing up to the omnipotent Thanos after everyone else has fallen in battle against him.
Jim Starlin deserves one for killing off half of the universe, pressing the reset button, and not having it be a detraction to the story. The reset only happens because of the selfish actions of another character. Sure, the reader knows that the dead heroes—including the Fantastic Four and pretty much all of X-Factor—aren't really going to stay dead, but it's done in a way that doesn't feel inevitable.
Even putting aside that Thanos is nobody's idea of a pushover, and Mephisto's power isn't nearly as great outside of his home dimension, the denouement of The Infinity Crusade, where Thanos fulfills his agreement to give Mephisto a Cosmic Cube... but follows through with Exact Words and makes sure it's inert first. It's not just that Thanos gets away with a Did You Just Scam Cthulhu?... it's the fact that he then pulls out a Badass Boast to taunt Mephisto, and gets away with that, too.
Thanos: Even devils should beware when bargaining with Thanos of Titan.