"I think it would be regrettable if I were to drink or smoke weed with either (TROPIC THUNDER co-stars) Jack Black or Ben Stiller because they would say, `Wow, I got stoned and I have a buzz,' and I would be off to the races and in jail within three days." Robert Downey Jr. insists his notorious addictive personality wouldn't be able to deal with just a small hit of marijuana.