It's a pretty normal thing to do, you know. Jerking off in the shower, because you're relatively alone. I mean, not these showers, but showering at home.

[Who is he kidding people might jerk off in these showers too, everyone gets a little pent up even if they're in a hell hole. Working his hands up Iwaizumi's sides, then dipping them forward to close that little bit of gap between them and pull Iwaizumi flush to his chest, Oikawa stroked lathered hands up and down his chest and abdomen, kissing his neck more eagerly.]