i saw a show once that was pointing out all the clues in the show Scooby-Doo that suggested that Scooby and Shaggy were high.

A couple of the ones I remember:
In one episode the "radiator breaks" in the van, and Scooby and Shaggy pop out of the back of the van along with a cloud of smoke and they're both laughing.

Shaggy and Scooby are ALWAYS hungry, the muchies?