We have to highly disagree on the 'became a douche' with Opal part because we have different ideas of characterization here. But the movie plot in book 2 I agree in.
Yeah we've had this discussion before, and I still don't agree with you. If you want to argue this scene doesn't define who he is, then that is fine. I'm not trying to argue it is. However, in a show where we don't get a lot of screen time for Bolin, this was just another scene that rubbed me the wrong way with his behavior. Which was a major shift from Book 1 Bolin.
The way he talked about Opal was totally douchey. And his cocky/arrogance was a carry over from the mover plot (which made him a douche bro). So even if you want to argue I'm reading too much into the scene, at least for me it's the overall context for the character that bugs me and where they took the character.
I was ready for Mako to be the next Zuko way back when LoK was announced.
He never even came halfway floe.
All side characters in this show (save for Tenzin/Lin) are a waste of potential. To be clear, I'm not trying to argue that Mako is a great character. He's not. He'll always be weighed down by his bland personality and the writers not knowing what to do with him (although, they don't know what to do with most of the characters on this show). However, I look at Mako in Book 1, and I see them taking steps to correct the characters problems. Even if it only slightly moved him in the right direction, they did move him.
Bolin on the other hand, had a major shift to the wrong direction. And I'll never understand why they took one of the best side characters from Book 1, and did what they did to him.