[It's weird, that's for sure. Even now it's hard to see (or rather, feel) the appeal of this, but given that it's so common he just... tries to calm down enough to wait it out. As soon as Oikawa starts pressing his finger in and out even just that little bit his stomach constricts, tensing up his abs as a means to hold himself in place.
no subject
He doesn't want to squirm away.]