Can I use a Humiliate on an opponent who uses their turn to First Aid to prevent their life gain?
Yes, but the number it stops depends on whose interpretation of the rules you're using. Jeff Tidball says it only stops one first aid if multiple are played. John Nephew says it stops all of the ones played.
And I'm the one who's right, by the way.
I fear inciting the wrath of one so high in the hierarchy of Atlas as Jeff Tidball, but I must say I agree with your opinion on this one Mr. Nephew.
[i]Dear John Nephew:
I climb up on top of the Atlas Games logo in the upper left-hand corner of the forum page, and, from that height, leap out of your computer monitor with both thumbs extended, aiming for your throat and gouging mercilessly. While you're gasping for breath, surprised and in pain, I grab the computer monitor I just leapt out of and smash it to bits over your head.[/i]
That said, after re-reading the definition of Humiliation, I've got to agree that Humiliation cancels an entire action, and so therefore can work on a stack of First Aids at once.
However, that said, I've got to wonder why Humiliation doesn't work on other card combinations, such as Grab + Powerplay, which are arguably a single "action" unit just as much as a pair of First Aids are.
That I'll agree with. I always played the humiliation as a card that stops an entire sequence. Though it doesn't really make sense in the case of a powerplay or an uppercut^2, I always figured that as long as you humiliated the attack that followed the sequence of events (for instance, a hail mary that followed a grab), it really doesn't matter that you got grabbed. You humiliated the thing that actually did damage and struck back, which means you'd probably get out of the grab by default.
My take on it has been this: With First Aid, you play them all at once. "Three first aids." You don't play first aid, first aid, first aid (looking around, cringing as you so typically do, hoping not to provoke any response from each). On the other hand, the various Grab + sequences involve playing a card, offering the opportunity for a response, and then (possibly) playing another card. "Grab," I begin. "You gonna dodge, you wuss? No, then a PowerPlay. Like that, little girl? OK, how about this Hail Mary?"
I agree that it is that break in the action, that opportunity for defense, that sets the Grab apart from the First Aid.