Amanada argues that Y Tu Mama Tambien is a lousy movie because the character of Luisa is the ultimate Manic Pixie Dream Girl. I'm not going to mount an unqualified defense of the film, but I've got to resist that characterization.
The Onion defines the MPDG as a "sentient ray of sunshine sent from heaven to warm the heart and readjust the attitude of even the broodiest, most uptight male protagonist." The MPDG is the free-spirited stock character whose main function is as a psychological tonic or crutch for the nice guy male lead, i.e., the full-fledged human whose fate we're supposed to care about for its own sake. Natalie Portman plays an archetypal MPDG in Garden State.
Onion AV writer Nathan Rabin coined the term to describe Kristen Dunst's character in a scathing review of Elizabethtown:
The Manic Pixie Dream Girl exists solely in the fevered imaginations of sensitive writer-directors to teach broodingly soulful young men to embrace life and its infinite mysteries and adventures. The Manic Pixie Dream Girl is an all-or-nothing-proposition. Audiences either want to marry her instantly (despite The Manic Pixie Dream Girl being, you know, a fictional character) or they want to commit grievous bodily harm against them and their immediate family.
We feminists roll our eyes at the MPDG character for obvious reasons. It's an annoying form of objectification most commonly perpetrated by male writers who are smugly convinced of their own progressive sensibilities. They think they're better than the guys who leer at pinups, but the MPDG doesn't have any more depth. The MPDG is wish-fulfillment for all those nice guys out there who just want someone conventionally beautiful to see their inner beauty and appreciate their mix tapes. The writer doesn't want you to doubt that the guy totally deserves her--maybe not in the sense of being handsome, successful, or charming. But, see, those are bullshit social norms that are keeping our hero down, which is why he needs a crazy girl to truly appreciate him in ways that shallow cheerleaders cannot. Lazy writers think that if they make the girl a little daft, they can skip the part where they explain what she sees in him. She's whimsical, that's why!
Whatever else you can say about Y Tu Mama, and it's not a flawless movie by any means, Luisa is no MPDG.
NB: If you have not seen this movie and think that you might ever want to do so, stop reading now. Massive spoilers follow.
Here's the basic plot: Tenoch (Diego Luna) and Julio (Gael García Bernal) are best friends, graduating seniors from Mexico City who find themselves at loose ends when their steady girlfriends leave for a summer in Europe. At a country club wedding, they meet, and are smitten by Luisa (Maribel Verdú), a beautiful woman in her late twenties who is married to Tenoch's even older cousin. In a bid to impress her, they invite her on a road trip to a fictional beach paradise called la Boca del Cielo.
She initially blows them off. Later on, in the throes of an existential crisis, she decides she wants to go after all. So, the three of them get in a station wagon and set out for the beach.
One of the things that's bothering Luisa is that her husband recently confessed to being a serial philanderer. Revenge alone would explain why she decides seduce her brother's pissant cousin and his BFF. Again, stop if you don't want to hear the spoiler... We later learn that Luisa decided to leave her husband and take the road trip after being diagnosed with terminal cancer, a fact she never shares with the boys.
Granted, the fact that Luisa's reaction to her diagnosis manifests itself in a desire to sexually educate immature 17-year-olds who love jerkoff jokes should raise our MPDG index of suspicion. But Verdú's performance is rich enough that you never doubt that she's getting off on the whole process. Partly she's rebelling against having been a good girl all her life. Maybe she wants to leave some sort of legacy by giving these guys an initiation they'll never forget. Luisa's character is outwardly charming and free spirited, Verdú's performance still hints at a certain amount of manipulative creepiness that you don't see in a MPDG.
By definition, a MPDG is a foil for a sensitive but misunderstood hero. Tenoch and Julio are neither sensitive nor misunderstood. They're both relatively popular guys who are cheating on their beautiful high school girlfriends. Tenoch and Julio have a few "alternative" pretensions, but they're more budding frat boys than anything else. Luisa doesn't see their inner beauty, she sees them as likable but easily manipulated. They are a means to her self-actualization, not the other way around.
Moreover, their pathetic self-centered horniness is the central joke of the movie. Time and time again, the joke's on them because they assume that Luisa is an MPDG who thinks they're special, only to be disappointed because her desires only sometimes coincide with theirs and because, unlike their girlfriends, she feels no compunctions about bruising their egos. Eventually she lures them into a threeway. The next morning, the boys wake up with horrible hangovers and gay panic. By this point Luisa has already ditched their sorry asses, having gotten exactly what she wanted: A sexy road trip and a ride to a beautiful beach. They never see Luisa again.
If this was a MPDG movie, the caper would have been win-win. But Y Tu Mama shows the episode exacts a real toll in the guys. The boys, who were once as close as brothers, can't face each other again because they're weirded out by having transgressed a macho taboo of actually touching each other--even though we've seen throughout the movie that they're perfectly comfortable jerking off together, sharing sexual fantasies, having sex in the same room (IIRC), and doing basically everything but having sex with each other. At one point, Luisa even sarcastically points out this homoerotic undercurrent in their relationship.
A MPDG character would make these boys into better people, but Tenoch and Julio don't learn anything. In the end, they allow homophobia, jealousy, and class differences to erode their friendship. A MPDG would have given them a special adventure to cherish for the rest of their lives, or at least some kind of lesson to live by. At the end, they still don't get it.
It's only well after Luisa's dead that they realize she didn't just sleep with them because she was a free spirit. She was a dying woman working out psychological issues they never guessed at, and couldn't have grappled with even if they had known.
We're supposed to think that Luisa grasped what was really important and seized it for herself at the end of her life. At the end, she defies convention and dies happy and while the boys are poised to slouch into boring, conventional adulthood.