A character is implied to have some unusual sexual preferences and fetishes (but the show is never explicit about it).
A character lies about being sexually abused by his uncle, but it is played for laughs.
Some episodes show male characters stripping or very little to no clothing (occasionally objectified by women), but played for a combination of comedy and heterosexual female entertainment.
Dialogue is present on the subject of sex, relationships and couples are shown post coitus several times putting their clothes back on.
Pierce talks a few times about buying hookers and other companionship (jokingly).
There are a lot of love triangles and love interests, but nothing is visually graphic. However, there are fairly frequent jokes about sex though, and Jeff and Brita are very amorous and "hook up" with a lot of people throughout. They talk about these situations with some mild "off color" dialogue, but nothing too bad.
A character has a pregnancy scare and her tryst with another character is discussed. Also, her husband is cheating on her with a "stripper" (nothing shown).
In Season 1, Jeff plays billiards naked and the camera shows about as much skin as possible without showing anything graphic.
There are some episodes that show female characters in tight-fitting or revealing clothing behaving in a suggestive way, but this is played for a combination of comedy and titillation.