My experience is that women often retire to the restroom together as a pretext to talk in a place where the men can't go. If they had nothing to talk about, they wouldn't have gone together - particularly since they had only just met for the first time that evening and Lureen in particular doesn't seem to be enjoying anyone's company.
I know that this may only be a plot device to leave the men alone so they can have their discussion, but I am always left wondering in this scene what was they reason Lureen and Lashawn had to go someplace private to talk?
Women tend to go to the restroom together just because they're sociable. Sometimes they have something specific to discuss or gossip about, but many times a woman headed to the restroom will just routinely ask the other woman if she wants to join her, with no conversational agenda. In this case, particularly, as the two couples were leaving, it would be natural for the women to stop in the restroom together on the way out.
IMO, it's probably reading too much into the scene to think that Lureen and LaShawn were discussing anything private or significant. For one thing, as they emerge it sounds like LaShawn is just babbling on as usual. For another, what would they have to talk about that would BE significant? Their unhappy marriages? Their husbands' gayness? the subtle flirtations going on at the table? No way -- they don't know each other well enough, and they're both in denial anyway. And anything other than that -- Lureen's concerns that the sagging agricultural economy might hurt the farm implement business, LaShawn's confession that she finds Roy Taylor hot -- wouldn't be significant in terms of the story.
Mainly, their absence gives Jack and Randall the opportunity to talk about something that IS significant.
