Beavis and Butt-Head/Radar

Beavis and Butthead have moments that get by, even by MTV standards.

In the episode "Dream On", you can hear Beavis mumbling "Fire, Fire"
To elaborate, this was after Beavis' catchphrase was Bowdlerised (to "fryer, fryer") because of the episode of actual pyromania it was falsely accused of in Real Life.
Not only that, in "Wet Behind the Rears" and "Buff N' Stuff", the boys are in the nude near the end. In the former, it was a trap set up by McVicker and Buzzcut to embarrass the boys for all the trouble they cause them, while the latter has Beavis sent to the showers with Butt-head whipping Beavis with a towel. The main characters are teenagers and they're in high school.
In some episodes, Beavis is seen trying to light a cigarette, like he did at the end in “Murder Site” despite being a teenager.
In “Buy Beer”, the boys actually buys what they thought was beer, but it wasn’t non-alcoholic.