After the end credits of season one they show the Cartoon Network logo and Dee-dee is dancing but then Dexter in a robot suit busts through the logo and looks to his left and right.
In the episode "Sdrawkcab" (backwards), the opening credits run backwards.
After the credits of the 2001 season, Dexter and Dee-Dee are inside the Cartoon Network logo, Dee-Dee presses a button that makes Dexter explode.