Mild Innuendo.

Sex is mentioned in an episode a few times, boys want women to wear bikinis in the same episode. A line is "we are human beings, not some sex toys." One of the characters is a feminist.

Boys make comments on female appearances and relationships and kissing are both common

Zack and Slater get into a brutal fight in one of the later seasons over a girl.

In one episode a character abuses caffeine pills

One episode involves a special guest who is seen smoking marijuana

There is an episode where the main characters are drinking