Not speaking from personal experience here but I have heard the following might be good under the influence:
Pink Floyd - The Wall Fritz the cat (not sure if that is available on DVD) Heavy Metal The X-files series - and the Movie too Any and all Star Wars films
That is all I can think of for now, seem to be experiencing a short term memory loss...
On the night of my bachelor party, my best man screened for us "Monty Python and the Holy Grail". I'd seen it before and couldn't get it, but he told me that if you were completely lacking in sleep or stoned (or both), you'd get the humor. We didn't get stoned that night, but we were up all night long, and I got the humor!
Well...it has been at least 13 or 14 years since I gave up the wacky tobacky but when I did enjoy scooby snacks some of the favorites I remember me and my friends watching...well...kind of remember...were Eraserhead - Clockwork Orange - The Wall - Heavy Metal - Fantastic Planet - Evil Dead 2 - Hellraiser - Dolls - Barberella - 2001 - Forbidden Planet - Liquid Sky - Repo Man - The Song Remains The Same - Roger Rabbit - Cheech & Chong - Dawn Of The Dead - Tommy - Altered States etc. etc.
...oh, and of course The Three Stooges!
P.S. Loooong before I ever got stoned I "got" Python....but I'm not sure if that is a good thing or a bad thing.
Not something I've ever done (I've seen way too much damage done to friends).
However, to answer the question set, a friend swears that he developed a phobia of rabbits from watching Night of the Lepus. So maybe any film that doesn't feature giant rabbits wrecking unconvincing model towns can be recommended. Not sure that reduces the field all that much.
I also know a guy who knows a guy whose brother worked with a guy whose auto mechanic once told his sister in law's best friend's dog walker that this film also entertains highly when one is on 'shrooms. But that's just what I heard...
I have never touched a single drug in my life, besides medicine and Tylenol, but my brother has done more than his share and he swears that Pink Floyd The Wall makes total sense if your out of your gord.
Night of the Living Dead would be a good one I would think, especially with a stoned friend who's never seen it, you could tell him it's the news and it's really happening and have fun watching him freak out.