I've always interpreted it as marital bickering, no so serious as humiliating each other publicly - neither of them are happy in their marriage and are tired of pretending, although obviously not tired of it enough, because they are still married. Jack seems tired - tired of the marriage, tired of waiting for a whole lot of nothin' from Ennis. Lureen took a swipe at Jack, Jack does so right back. She gives LaShawn a put-down too, about her more prestigious sorority, as mentioned above, but those days are behind her now. Lureen appears to now be a disappointed and bitter woman. When Jack asks "Wanna dance?" I have always thought he was saying it to Randall, and LaShawn just assumes he means her, and he does actually mean her, and they dance. Almost as if he's tired of hiding who he really is and whether said jokingly or not, he's saying it to Randall, because he seems to look right at Randall, and Randall got the message.