Of course Oikawa liked to be the one in control. Then he could spin the situation however he liked and a good deal of the time anyone around just had to deal with that fact. Now that Iwaizumi was the one holding what happened in his hands, naturally Oikawa hated it. And he damn well knew it. Though, for him this wasn't a matter of a power struggle, not in the same way. Oikawa would take the chance to make nothing of it, if he could. He still might laugh it off if he could get away with it... not that Iwaizumi was about to let that happen.
Sure, he might never hear the end of it for even threatening to leave Oikawa there, but they both knew he wasn't really going to. But the threat kept their typical dynamic in check… and it made Oikawa squirm after being a punk. Probably more importantly… it gave Iwaizumi a chance to gather his thoughts. It might not have helped because in the end… he didn't know for sure what was waiting after. Something more complicated, sure, but in what way, he couldn't say. And if Oikawa did just brush it off like nothing, well… either way he got an answer to a question that had been hanging in the air for too long now.
Oh, he was sure Oikawa would be ticked off when he got back, but also begging and apologetic because he didn't want to get left there again. The shift from cocky Oikawa, to blubbering and back again might give anyone else a case of whiplash, but not Iwaizumi. And like Oikawa hid behind a certain facade, so did he. His bouts of violence and indifference, then aggressive mothering knowing how obsessive a certain idiot in his life could be. It apparently made them painfully obvious to everyone but each other.
Rolling his eyes, Iwaizumi put in his own effort to maintain that push and pull that kept them just far enough apart, without treading into what were deemed dangerous waters. "You have a shitty sense of humor," he said as if he didn't himself, leaving his best friend to squirm there under the mistletoe like he wasn't going to come back. He supposed he very well could not have… but after going to some magic country for him, Oikawa should know he was always going to.
Now that he was back in front of him, faced with the opportunity for a kiss, the nerves crept back up. Unless you think you'll like it or something, was his exact fear… one he had some gut feeling was shared. He knew Oikawa, whether the other boy liked it or not. "I think you're afraid you'll like it," he shot back with a smirk that could do nothing to hide what was behind his eyes. He wasn't as good at that as Oikawa was. There was no… just pretending like it didn't happen after, he already knew that. There would be something to be said about this afterwards, one way or the other. Luckily, it was easy to disguise his hesitation as more taking his time to make Oikawa uncomfortable. Closing the gap between them, Iwaizumi was annoyingly reminded how much taller Oikawa was than him. He wasn't going to hear the end of it. The way he had to stand on his tiptoes, a hand on Oikawa's shoulder, to reach properly as he leaned up to kiss the idiot before he changed his mind or lost his nerve.
More annoyingly still… Oikawa was right. He did like it and when he pulled back, it showed immediately in his eyes. His heart was racing and some crazy impulse told him to do it again, but was ignored. For now. He didn't want to end up getting brushed off, but if Oikawa didn't say something obnoxious - or you know, negatively obnoxious - and initiated the next one… that would be another thing.