One of the things about FFX is that Tidus is a moron. This is not news. The thing that really gets on my nerves, however, is that Tidus is a moron and the rest of the party doesn't care. Or doesn't notice. Either way, Tidus is a complete moron and he gets away with it.
In FFXII, Vaan is also a moron. And tactless. ("HEY FRAN how old are you," "Oh, like we didn't recognize you even though you're our princess!" "...I noticed.") However! The party actually gets irritated at him. Penelo tells him to grow up; Balthier tells him "Smooth;" Larsa says, "That was surprisingly rude;" Fran, Basch, and Ashe usually either respond sarcastically or just shake their heads. The point is, though, the party members react to Vaan similarly to how I'd expect people to react. He's an idiot and the other characters notice.
When you add in the fact that FFXII - so far as I've gotten, at least - hasn't had any truly irritating cutscenes - read: Tidus laughs, Yuna learns how to fly, anything else relating to Tidus and/or Yuna - and anyway, if I don't want to see it, I can hit skip scene, it rather avoids the main things I hated about FFX.
If only there was a version of FFXII with CTB. Or FFX with cutscene skip because I quite liked the gameplay; I just couldn't stand any of the characters except possibly Rikku.
I still want to shoot Vaan in the face. And I'm pretty sure he doesn't get significantly better since he's still an ass in Revenant Wings. I like the rest of the party! And Larsa, who is a guest often enough for him to count as part of the party as far as I'm concerned. I just... can't stand Vaan. Penelo doesn't deserve him, she really doesn't.
The only decent thing Vaan's done so far in FFXII and FFXII:RW that I've seen is hit Llyud when he's being apathetic and annoying. I quite like Llyud, but dude he needed to be slapped. Doesn't make Vaan any less of an ass, though.
ETA: Fran's ass has rather impressive jiggle physics.
ETA2: I have gotten farther in FFXII and Vaan is slightly less of an insufferable jerkass.