Of course Tomoki isn't turned on! That situation is a freaking nightmare. It's not his fault that he doesn't have AutoDick.
Here's the situation:
Tomoko (the reason why a normal guy, straight or not, would want to give up on women forever, especially a brother she has tormented for a long time)
Koto (enough to make him give up on women forever)
Akari (pretty nice, but at unexpected times makes him want to give up on women forever)
Sayaka (basically blank, but puts him in a position where he wants to give up on women forever)
Yoshida (she's okay, even if she's a delinquent, but he and she get into seriously embarrassing situations)
He loves sports, an orderly life, and having his own safe room. He gets the first; the second two are denied him.
He has no desire to stick it in a light socket. Who can blame him?