He asked Sam a million and one times to just leave him and Josie alone in the bed to talk but Sam wouldn't go and that was getting John wound up and then when Sam finally did go he was still looking at them through the glass, Sam just wouldn't leave it. It wasn't only John in the shower talking about Sam, JJ and Dave were too and John did say he was going to talk about it with Sam later on sooo but when the argument started, JJ and Dave didn't get involved and Sam never said anything to them two
John and Sam do really like each other and it was just all that anger and stress came out but they are friends, you can see they are.