There is the possibility that Frank is gay and in the closet. Consider that all three are standing naked in the bathtub. Karina is washing them off, Jenn is playing with Frank's penis without producing a reaction. Jenn steps out of the tub. Before Frank steps out of the tub, he covers his penis with his hand -- like a little boy -- so that Karina cannot see its soft state.
It is Jenn who removes Karina's bra when they are in bed together, as if to say, 'its okay Frank, you can play with her.'
It is Jenn who takes off her panties, pills the covers half over, and gets on top of Frank. No response from Frank.
He was more interested in his song playlist than in either Jenn or Karina. No focus at the task at hand. And even if alcohol and rolled paper resulted in erectile dysfunction, he has a mouth and fingers which were not paralyzed.
Do you think if it was Daisy, Jenn, and Ben (Benji or whatever his name is) together in that bed last night, that Ben would have stopped every two or three minutes to change the music?