Sometimes there is not much needed for quarrel to happen. It can be an inaccurate word or a simple misunderstanding that will bring up something from the past, forcing people to point at each other's mistakes simply to justify themselves. But it requires much more to bring peace. It can be simple "Sorry" that will take a lot of courage from someone to say or something else to apologize. Dean always picks "something else". And he always knows what it will be by the very moment he's crossed the line with Sammy. As Dean is not good with words in general he will do something that does not require ones. Normally, it would be a prank. To show that everything is moving on and that they are still family, no matter what. But if it was something serious like when Dean says something extremely hurtful to his brother and gains sad and silent look as a respond he will have to put some more efforts. It must be something really special. Or not really special but valuable that will show how sorry Dean is.