Theory regarding the most recent episode:
Louis wasn't necessarily going for the whole
MPDG vibe with Louie's girlfriend, but more trying to encapsulate an entire relationship in the span of one and a bit episodes. The weird little foibles from Posey's character didn't happen (in context of the life of Louie's character) within one night but spread over a period of months (over which she'd have been considered "normal"), and the show chose to put all of this into the 1-1.5 eps rather than having it be a series-long arc that loses it's impact over time.
I think it fits kinda nicely into C.K.'s MO, too.
Of course, I could be barking up the wrong bush, but there are a few little things that lead me to think like this. One that's just popped in my head (after pondering this theory) is the part where the guy in the pool hall is checking her out from behind the glass. Could well point to Louie and a possible insecurity with cheating, despite it never having been portrayed any further than that in the episode itself. Maybe not, but it's another thing to think about.
Anyway, I'm just gonna leave that here. Discuss.
Or not.