The show isn't out to promote any particular message other than humor, but the main characters' friendship is a strong one. Songs and episodes mock misogyny, xenophobia, and other social/cultural issues.
Some dating and kissing, as well as talk about the possibility of sex. In one episode, Bret has sex (nothing graphic shown) with an aggressive date; in another, a fan proposes a three-way to the guys. But overall, most of their dating attempts fail.
Regular profanity like "s--t," "f--k," "a--hole," "dick," etc. Since it's pay cable, nothing is bleeped -- but it's worth noting that Jemaine and Bret themselves rarely swear, opting instead for terms like "motherflipper" and "mother ucker."
Occasional social drinking and discussion of drug use. In one episode, the guys are pressured into doing a "sixteenth" of acid -- which leads to a trippy song-and-dance sequence.