i actually enjoy the break of class between maekar and dunk, and dunk receiving no punishment for it.
dunk himself never really addresses or treats maekar as a prince. when he first meets him, it's when he is spying on the targaryens and while he fumbles around with his words and all, his honorifics and respectful tone are toward baelor. the one he regards as a prince and treats as such is baelor. the one dunk speaks to as if he is addressing someone from the royal family is baelor, nor maekar.
toward the end, when maekar and dunk have their conversations, dunk addresses maekar very informally. Specifically when Maekar offers Dunk a place at Summerhall, Dunk, "I'm done with princes", would be taken awfully by almost any other Targaryen man. Meaning, other Targaryen royalty would've seen Dunk's tone as very dismissive and disrespectful given what Maekar just offered Dunk, but Maekar, did not get upset. He just, accepted it. If I were to say one thing he probably was upset on behalf of Egg, which is most likely one of the reasons he refused to allow Egg to go with Dunk. Because while he didn't feel Dunk insulted him with that, 'I'm done with princes' line, despite Maekar's offer being genuine and displaying his own vulnerability during his grief, Maekar probably knew Egg was listening.
Another thing I notice is that aside from Aerion, the Maekarlings themselves also break class and protocol with Dunk in a similar way to their father. They talk to Dunk like he is one of them or they are one of him, Daeron is drinking and speaking to Dunk and there are no honorifics or anything used, he just doesn't gaf. And then there is Egg. (it is a huge contrast to Valaar whom is very dismissive and short with Dunk, and treats him as a Targaryen prince would normally treat a small folk. And Dunk also views/addresses him as a prince. )
but the point is that, while maekar struggles with his own classism, dunk often time speaks to him out of turn and also addresses maekar as if he is not speaking to a prince. even more so after the death of baelor, the formalities are just not there, on both ends.
after dunk initially pulls the 'im done with princes line', he goes back to seek out maekar and HE, requests Maekar's presence. A small folk not only requests an audience with the prince, but he is granted it without having to go through any hoops and aside from Maekar being petty on Egg's behalf, there is still a breaking of class and formalities. Dunk is not talking to Maekar like a prince, and while Maekar does deny Dunk taking Egg on his journey first by saying, 'he is the blood of the dragon', he quickly refutes that and says, 'he's my las son'. a vulnerability that is rare for a prince to display to a commoner. and he is on the verge of tears when he is saying this.
the point is that while there is a thin veil of prince/small folk between those two, the lack of formalities and respect toward a prince between them is very unique. because they speak toward the end as equals, and even beofre, when Dunk is referring to the brother's in an honorific way as if he is speaking to nobility, it is usually Baelor he is speaking to. He views Baelor as a prince, as this untouchable and pure being that is on a different plane than him and everyone else. Almost a madonna like figure.
But Dunk does not view Maekar in that light, nor addresses him as such. His talks and the way he regards Maekar is a lot more human and equal and Maekar never does anything to correct the way he is addressed by Dunk in such a casual way.