Continuity mistake: At the diner where the Jason Burgers are being sold, Ward complains about not being able to make the patties correctly, so Joey demonstrates. As she makes the two eyeholes with her finger, the patty changes places on the counter between shots. (00:20:20)
Continuity mistake: When the Coroner is stopped by the two security guards, he places his pizza box a bag of drinks down on the table. One guard then pats him down and then in the next shot the position of the drinks bag on top of the pizza box has changed. (00:14:40)
Continuity mistake: When the light bulb explodes, Agent Marcus takes the old, burnt bulb away, and puts it on top of the metal ladder she's standing on. In the next shot she descends the ladder and folds it up, with the old, burnt light bulb having mysteriously disappeared. (00:02:50)
Continuity mistake: When Steven fights the possessed sheriff at Diana's house, they hit the table knocking the lamp on the floor. You hear it shatter yet it's still lit.
Continuity mistake: When the coroner sees Jason's heart beating, from shot to shot he has a little blood, then a lot, and then just a little again, but when he goes to actually eat the heart there is a lot of blood smeared on his cheek and face. (00:12:30)
Continuity mistake: The pole that impales Deborah moves from going though her chest just below her boobs, to much lower down, in her waist between shots. (00:31:55)
Continuity mistake: When Josh transfers the Voorhees creature into Robert's mouth, blood runs down Robert's right cheek as this transfer is made. Once Robert then wakes up as Jason, the bloodline has swapped cheeks. (00:56:40 - 00:58:00)
Continuity mistake: When Randy drives out to pick up Steven, Randy takes off his police hat and puts it on the hood of the car. Randy then punches Steven, and in the next shot you can see the police cap has vanished from the hood. Cut back and it's there again. (01:03:15)
Answer: There isn't much of a feasible in-movie explanation. In truth, the entire scene was added by the director because he felt the movies were pretty sexist in that it was mostly women who were either nude or sexualized. Thus, he added an inherently homo-erotic sequence involving one man shaving another stripped man to "level the playing field" so-to-speak. The only real explanation I could think of is that maybe the creature just thought it'd feel uncomfortable transferring to a man with a mustache. But even that's shaky at best.