It's the drug PSA that defined a generation. Enjoy the entire 27 minutes right here, and check out some other anti-drug moments from the wonderful world of animation... they're pretty trippy.
Here is the entire 27 minute anti-drug PSA starring just about every relevant cartoon character that was working the beat in '90:
For a more entertaining, abbreviated, to-the-point version, check this shit out:
Here's an attempt by Hannah Barbera to discourage drug use, it makes a lot more sense if you are on heavy amounts of drugs while watching it: