Sexuality
Sex is given immediate importance in Y Tu Mamá También, with the opening scene showing Tenoch making love to his girlfriend. The sex is fervent and hurried, characteristic of the young people involved as they discover one another's bodies hurriedly and ecstatically. Sex continues to be a major theme throughout the film, as Tenoch and Julio embark on an odyssey with the woman of their dreams, Luisa.
While Tenoch and Julio are incorrigibly horny and immature about their own sexual urges, Luisa is an older woman and more settled in herself as a sexual being. She seeks to teach the boys a thing or two about sex, and in so doing liberate herself from her horrible marriage to Jano, and experience pleasure before her inevitable death. Sex is a discovery for Tenoch and Julio, but for Luisa, it is an escape, a chance to transcend her worldly woes and experience something more.
Sexuality takes many different forms and has many different effects throughout the film. In the beginning, we see that sex is a major preoccupation for the two friends, as they have sex with their girlfriends, masturbate beside one another at the pool, and comment on the attractiveness of their respective penises. In this section, sex is a schoolboy's game, an innocent if consuming preoccupation. The friends' views on sex change once they are on the road with Luisa, each vying for her erotic attention and eventually, hashing out their sexual betrayals. The friendship is ruined when the boys reveal that they have each slept with the other's girlfriend, and they struggle to reconcile. Then, when Luisa seduces them both, they end up sleeping together, kissing passionately, and waking up naked alongside one another. Their shared sexual experience only drives them further apart, and they return to Mexico City nearly completely estranged. Thus we see that sex begins as an innocent boyish interest, before blossoming into a more adult and charged affair. While Luisa maintains a straightforward perspective on sex, this cavalier attitude does not influence the boys, who become afraid of their own desires, and the erotic experimentation that they indulge in their travels cannot endure their return to the city.
Death
Death is a consistent theme throughout the film. Most centrally, death becomes important when we learn that Luisa was dying of cancer all along, and stayed with Chuy and Mabel in order to die near the ocean. She is alternately joyous and inconsolable about her lot. In one moment, her deadly fate strikes her as debilitating, and in the next she is filled with a love of life, "carpe diem" spirit inspired by her knowledge of her own impending death.
Additionally, we hear the stories of many deaths throughout the narrative. First, we learn about the death of a construction worker which causes a traffic jam, then later see a cross on the roadside respecting the death that occurred ten years earlier from a car crash. Additionally, Luisa casually tells the boys the story of her first boyfriend and his death in a motorcycle accident when he was 17. The film follows characters who are eager to experience life, and along the way they are reminded of the ever-present reality of death and finitude.
Class
The opening of the movie highlights the discrepancy in class between Julio, who comes from a middle-class family, and Tenoch, whose father is a high-ranking politico. While these differences do not seem to affect the boys' friendship, tensions erupt when the two of them find out about one another's flings with their girlfriends. In a blowout fight, Tenoch calls Julio as a "hillbilly" and Julio calls him a "yuppie." In this moment, the boys are pushed to see one another only through the lens of their class position, and when they return home, they go in very different directions, with Tenoch studying economics like his rich father wants him to, and Julio pursuing a biology degree.
Additionally, class disparity in Mexican culture more generally is alluded to throughout. The construction worker who was hit by a car was hit while he was trying to get to his menial job more efficiently, as infrastructure did not support his commute. As they pass through a town in their travels, Tenoch notes that it is where his nanny, Leo, is from. Then later, we learn that Chuy, the fisherman who shows them around Heaven's Mouth, will soon lose his job with the arrival of a luxury hotel in the area.
Travel
A rather obvious theme of the film is travel. When they first meet Luisa, Tenoch and Julio talk romantically about taking a trip to the beach, but she hardly takes it seriously. However, when her life is thrown into disarray, she calls them to tell them she wants to go on a trip after all.
What follows is a road trip movie, an adventure in which all of the characters do things they might not do in their normal lives. The open road liberates them from their self-imposed restrictions and allows them to feel an existential freedom that pushes them to places they never thought they'd go. The road liberates them, erotically, philosophically, for better and for worse. Thus, travel is a central theme in the film, the catalyst for the personal journeys that each of the characters goes through.
Homoeroticism
The over-the-top macho facade of Julio and Tenoch is stripped away in the movie's final sex scene, in which the two share a passionate kiss that undermines the societal perceptions of masculinity to which they desperately aspire. Their entire friendship is built around their shared masculinity, as they regularly call each other "faggot" and swap stories about their heterosexual affinities, but in this moment, the tension of their close friendship comes to a head. Drunk and turned on, their connection turns erotic, a turn that changes their relationship permanently.
Betrayal
At the start of the film, Julio and Tenoch seem like the best of friends. They are inseparable, always laughing and hanging out, sharing good times and enjoying their youth. Their friendship is so strong that it seems impossible that anything would break it, but on the road trip, they each reveal that they slept with one another's girlfriends. These betrayals are shattering and cause a huge breakdown in trust between the boys. While they were one "Charolastras" (the name for their tightly knit group of friends), they are now sworn enemies who resent one another. Thus, the major conflict of the film, the breakdown of their friendship, is the result of their respective betrayals, and their disrespect for the bonds that they have created as friends. While it seems like they might be able to heal from this betrayal, it ultimately drives them apart in ambiguous ways.
Societal pressure
Julio and Tenoch are two young men who want to continue to have boyish fun even though the world would prefer they grow up. At the time they embark on the trip in the movie, they are at the threshold of adulthood, about to go off to college, but still wanting to do drugs, get drunk, and have a simple good time, exploring their youth while they still can. Tenoch in particular faces the pressures that his domineering and powerful father puts on him, and wants to rebel against them. His father refuses to let him have a car unless he promises to study economics, but he wants to be a writer. He wants to be nothing like his father when he gets older, yet his father is a gatekeeper, preventing him from having the life he wants if he disobeys. Eventually, Tenoch does go on to study economics, and we see that he caves to the pressures placed on him by his father. While Julio does not have the same pressures placed on him, when he returns from the trip, he is also pushed to become more of an adult. Both of them feel obligated to pursue the lives prescribed to them by society, rather than the more free-spirited existences that they pursued on the road with Luisa. In the end, society and the pressures of the world win out and they do not take Luisa's advice: "life is like foam, so give yourself away like the sea."
