Tommy Chong says he wants to use his time on "Dancing With The Stars" to advocate for medical marijuana.  He said "I want to be the poster boy for the marijuana community".

We think he already attained that status in the early 80s with Cheech and Chong, but hey, nothing wrong with more PR!

He's 76, by the way, and still has it for sure!

Cheech made a surprise appearance during Chong's "Cha Cha" last night on the show's season opener...