HERE'S THE FULL STORY: As the only person here who has apparently watched the entire film (I guess I'm a horrible person lol), the context of the scene has to do with the fact that Jeff had an infatuation with the doctor and actually went for the exam under somewhat false pretenses.
Unlike the recent Ryan Murphy mini-series, one thing that this film has that the major Netflix production lacked is its basis on first person narrative from one of Dahmer's real life childhood friends, John “Derf” Backderf (https://en.wikipedia.org/wiki/Derf_Backderf), who personally knew him and was able to shed some light on the events of Dahmer's unfortunate childhood that might have contributed to him becoming the serial killer he did. He was able to help the producers gain access to Dahmer's actual childhood home in Bath, Ohio for filming (the house where the first murder was committed), and although the actual school they attended opted out of allowing them access for film production, a rivaling school in the same town was happy to have them thanks to Derf.
Anyway, the reason I went into this detail is, in the film, Dahmer is portrayed as obsessed with this guy, who turns out to be a doctor. He is the guy that Dahmer stalked from the woods, the first real world infatuation that he attempted to act on. In the Netflix series, Dahmer is portrayed as having an obsession with a much younger person closer to his own age. Given that the recent mini-series is based largely on newsmedia and “My Friend Dahmer” is based on a first person account, I wonder which one is more accurate? There is really nothing of major concern in “My Friend Dahmer” as far as gore. It is more of a comedic drama (i.e. Dahmer's version of “The Wonder Years”, if you will), with the ending portraying him picking up Steven Hicks, his first kill right after graduation, but it cuts to credits before anything is shown. The most you see is the taxidermy of animals.
While some feel there is no value in these types of films (and maybe you have a point to some degree), I think there is some value in the psychological aspect of it, as long as it is presented accurately. Perhaps films like this can raise awareness to the mentally ill individuals in our lives, and we can learn to recognize the signs (he had many) and instead of contributing to their demise into becoming a psychopath like Jeff was, we can find a way to help them and steer them away from that lifestyle. So many signs were missed, so many chances to change his life and prevent this from happening were missed due to fighting and careless parents, clueless friends who sort of encouraged him to go off the deep end, and other potential adult role models who chose to “wash their hands” of Jeff rather than try to help him. Regarding the implication that he ejaculated, that is not how I took that look from the doctor, I took it that he got hard on touch, and most doctors wash their hands after examining someone's genitals for obvious sanitary reasons. Generally, from discussions I've had with others on here and on other sites, most people who are going to get hard during an exam are already hard prior to the exam due to the atmosphere of the situation…in this case, it is implied he reacted to the object of his fetish touching his penis…something he'd fantasized about and masturbated to for months. Another relatable issue to current events was the fact that Jeff actually was gay, but was shamed to the point that…maybe…the drive he had to kill these men was to dispose of the shame he was conditioned to feel from having those sexual desires (he obviously didn't have a Zity to talk with other like-minded people about so that he was able to feel more normal). Could learning about his story help us to relate to homosexual individuals in our lives and not make them feel ashamed in the way that he was (although, admittedly, we HAVE come a long way as a society since that time period, thankfully.).
Anyway, if you have any care in the world about learning why Dahmer was the way he was, this film is (probably) the far more accurate source that I would encourage someone to watch. The new Netflix series was not nearly as accurate, and missed many details of things that actually happened. There are a laundry list of “mistakes” for the series, the biggest and most unforgiveable being the narratives of two real witnesses being composited into one woman portrayed by Niecy Nash. I don't even think there are five known mistakes for the film. The only couple of times they stray from the truth, Derf gave commentary on and gave a reason for the changes, telling what actually happened that differed slightly from the film (most of the choices were budgetary in nature).
In any event, for the purposes of this discussion, I, too, removed Dahmer from it and remembered it was Ross Lynch we were looking at in the doctor's office, not actually Dahmer. 😉