Consider this the nerdiest public service announcement ever. If you're like me, you were vaguely aware that at some point in Jeph Loeb's ongoing Hulk run, its semi-eponymous star, the villainous and uber-powerful Red Hulk, grabbed Thor's hammer Mjolnir and delivered Ye Olde Smacke-downe on the God of Thunder. You're also vaguely aware that this is more or less a total no-no -- no matter how physically strong Rulk is, only those who are "worthy" are even able to pick the hammer up. And there aren't very many such people: According to Wikipedia, you're basically talking half a dozen dudes, consisting solely of people who've wielded Thor's power itself, people who'd be present at a Thor family reunion, and Captain frickin' America.
What gives? I'd always just chalked this up to Jeph Loeb's, shall we say, zesty writing style, which tends to put a premium on big moments in lieu of story cohesion. But on his Formspring account, where at any given time around 25% of the questions being submitted to him are about whom the Mighty Thor could beat in a fight, editor Tom Brevoort has offered the official explanation of how a bad guy like the Red Hulk could wield Mjolnir.
...during a pause at one of our editorial retreats a few years ago, Jeph Loeb asked me if there were any circumstances under which the Red Hulk might be able to lift Thor's hammer. We batted it around for awhile, and after some thought I told him that I could foresee two circumstances under which that might work: 1) If Thor still had his hand within the hammer's thong or in his hand as well, so that the worthiness enchantment was defeated in that [Thor] himself [was] still in contact with the weapon, and 2) if the battle occurred in space where there was no gravity, and therefore the hammer was weightless. Jeph ended up using versions of both of these approaches in the story he thereafter wrote.
Well, that explains that! A quick Google search reveals that readers were skeptical of the zero-gravity loophole, which was advanced by the Red Hulk himself in the comic, but it seems it's canon. Apologies if this is all common knowledge in the Thor/Red Hulk debate community, but for an outside observer like me, it was a real "The More You Know" moment.