In fact, for some characters, including males, it was a rarity to be clothed at all.
Fiona is the character that can most commonly be found nude in the show.
Additionally, there were plenty of bare butts throughout the season.
Later in that same episode, Marty visits a gentleman's club where plenty of bare breasts are exposed and two women get intimate in the bathroom.
Though the show has a similar overarching story-line to Sex and the City, Girls is much more sexually explicit.
While the sex was not gratuitous, and you won't see full-frontal nudity, many sex scenes looked and felt authentic.