Treegasm is the fifth episode in Season 1 of Ugly Americans.
Mark Lilly meets a pair of tree creatures who are expected to participate in a public mating ritual sanctioned by the City of New York as a festival. Meanwhile a molting Callie Maggotbone demands the kinkiest kind of sex out of Mark, and Randall Skeffington loses his penis after visiting a movie theater.
Tourists visit Central Park for "Treegasm", a once-in-a-lifetime mating ritual between two tree creatures, or "treatures". The trees grow towards each other for decades before engaging in a ritual known as "screwing". Mark Lilly cannot understand why people care about two trees losing their virginity. Demon bureaucrat Twayne Boneraper has been appointed to be in charge of the ceremony, but gives the job to Mark and wizard Leonard Powers, as he has to spend four days to get fitted for a triple-breasted suit.
Meanwhile, demon Callie Maggotbone demands to have sex with Mark. Leonard explains to him that a female demon's body is so toxic that she has to periodically shed it for a new one, and that sex is the only thing that can ease her pain.
Later in Central Park, Mark introduces himself to the tree creatures, Neil and Nicky, as their "screwing coordinator". Mark remarks that it is refreshing for two beings to be so committed to each other as opposed to just having sex with strangers. Neil begins to feel anxious about the ritual, as Mark's remarks about having sex with others sounds more exciting.
As a result, Neil later breaks up with Nicky, as Mark has opened his eyes for other opportunities. Neil states that Nicky is predictable and that he wants someone crazy. Mark accepts Neil's change of heart, but Leonard later explains to him that Neil and Nicky are forced to mate because their roots run so deep that they encompass Manhattan. If Neil does not ejaculate soon, his roots could swell up and endanger the entire city.
Twayne assigns Mark to fix the problem, and Mark enlists his zombie roommate Randall to talk about his unhealthy sex experiences to Neil. Randall's stories horrify Neil and lead him to change his mind and go back to Nicky.
Later, "Treegasm" has become a public spectacle and has drawn huge crowds to Central Park. The event is about to commence, but Neil is nervous because of the pressure and the event's many spectators. His roots begin to swell, causing them to protrude from the ground and seize different buildings. The pressure causes his sexual organ to go flaccid, and Leonard quickly enchants him with a magical spell that acts like Viagra.
Meanwhile, Callie's shedding has hideously deformed her skin, and takes Mark with her into a portable toilet for her final intercourse before shedding. Just as Neil is about to penetrate Nicky, Callie sheds and reveals herself in her new form while standing naked amongst the crowd, mimicking "The Birth of Venus". The pressure causes Neil to suffer from premature ejaculation, and he ejaculates all over the park. The disappointed and disgusted crowd eventually leaves the scene. Later, when the crowd has left, Leonard enchants Neil with a spell to make him less nervous, and the ritual continues without spectators.
Meanwhile, Randall loses his penis after having sex with a female he met at the movie theater. After he fails to find it, he tries to get used to life without having a penis, but considers killing himself. However, he later receives a call from the police, who inform him that they have found his penis, but that it did not fall off - it ran away because it did not like the way that Randall treated it. In order to ensure its return, Randall must agree to several conditions, such as accepting it as an equal, which Randall gladly approves of.