Casey Tebo immediately captures ones attention with a snappy opening where Matt Bush returns home unexpectedly on his birthday to greet his girlfriend (Tristin Mays) only to find a note left under the toilet seat from the guy she spent the night with commiserating with him. In the ensuing scenes where they head over the border, Tebo creates a wonderful portrait of the dark and dangerous world into which the two guys have descended. Erik Palladino plays a street hustler with dubious government credentials who introduces them to no less than Aerosmith lead singer Steven Tyler as a shaman-come-drug cook who feeds them a blend of exotic drugs. After Matt Bush takes the shrooms he was advised not to, this leads to a tripped-out scene in a bar where Bush cannot be sure if he is hallucinating the barman pulling a gun on him, Matthew Willig taking a dump in the middle of the room, the stripper slitting the throat of a patron and Erik Palladino being blown by a tranny, all before a wild romp in a motel room with the two girls that has Britne Oldford punching Riley Litman in the middle of sex and ends with both of them handcuffed to their beds.
From the point that it takes on the feeling of a drug-induced nightmare, Happy Birthday! works rather effectively. Theres the bizarreness of Matt Bushs imprisonment with the two girls alternately attempting to tempt/sexually use him and torture him he is held in the closet in his underwear with tacks scattered on the floor to discourage him from emerging to at one point Britne Oldford pouring syrup over his body to allow chickens to peck him as a torture in between ominous threats that he doesnt want El Gato Inferno to have to come and the suggestion that things have gone wrong and Riley Litman has been killed.
Eventually ([PLOT SPOILERS], everything that has transpired is revealed to be a big set-up a la The Game (1997) in order for Riley Litman to give Matt Bush a birthday surprise he will never forget. The Game twist has started to become a cliche twist it was also used in the same years, Fear, Inc. (2016), which placed an amusing horror film homage spin on it. This works rather well. (It is also cleverly tipped in the opening minute where we get an appearance of a mocked-up poster for the film and some of Riley Litmans dialogue). The set-up is reasonably clever and not too improbable and credibility-stretching as some of these films get The Game being a notable example.
One of the more off-the-wall aspects of the film is Casey Tebos penchant for characters voicing wacky theories about pop culture in monologues. In the opening scenes, Riley Litman is on the phone discussing a remake of Gremlins (1984) and saying he wont do it unless he is allowed to bring the racist subtext out into the open. Steven Tyler has a monologue about racial interpretations of films like Rocky (1976), Star Wars (1977) and The Avengers (2012), while after being introduced head villain El Gato Inferno monologues about his love of Hollywood and father-son symbolism to be found in the films of Paul Thomas Anderson.