Under different circumstances, writing Rocky’s accent this explicitly might prove grating to a reader, but it works because it is 100% authentic to the character. Note the contrast in this scene between Rocky’s prizefighter way of talking and the subject about which he is talking. If he were bragging about being a tough guy, his pitted way of talking would somehow be less appealing. Rather, he’s going to bat for his pet turtles. 

Also, it’s a simple thing, but Adrian doesn’t say much and that’s how we know she’s shy.