Waylon Jeepers approaches Freakazoid and asks him if he'd like to see something "straaange and mysticaaaal?" Freakazoid pauses for a moment, then begins to scream "NOOOOOOOOOO!!! GET OUTTA HERE WITH THAT WATCH! LAY OFF THE POOR BEAVERS, WILL YA?!? SHEEEESH! YOU'RE A CREEP! GO AWAY! WE WERE ALL HAVING A GOOD TIME UNTIL YOU SHOWED UP, JEEPERS! UUUUUUUUGH! GO HAVE SOME COFFEE, WITH CREAM, OR SOMETHING! BECAUSE I'LL TELL YOU SOMETHING: THIS IS A HAPPY PLACE!!"
Not only did Freakazoid effectively show kids how to deal with creeps, but he secured himself as being awesome, forever.
Making this even better is that Paul Rugg, Freakazoid's voice actor, improvised almost all of that rant.
How about the end of that episode, where he makes out with the hottest of the girls who rejected him earlier, lampshading it by mentioning it's "shallow, cheap, and based sorely on hormones" before going back to sucking face?
During one episode, there's a short bit where Freakazoid's entire Rogues Gallery has Steph held captive in a high tower. Freakazoid proceeds to mow through the whole lot of them to save her.
The kicker? Freakazoid actually thought it was brilliant.
Pretty much anytime Cosgrove tells someone to cut it out, but special mention goes to getting the Warner Brothers (and Warner Sister) to behave in the crossover comic.