Though I've never saw "Plan 9 From Outer Space", but I've seen far worse films from the 1960's & beyond.  :P




*Any beach film like "Beach Blanket Bingo" & "Gidget"
*Any movie from the '30's that featured Shirley Temple
*Any movie featured Barbara Striestand like "Funny Girl"
*"Old Yellow" Very boring.
*"Red Balloon", I didn't get it.
*Any movie that was based on a musical like "Caberet"
*"Gone With The Wind"
*That one Disney movie about a guy who turned into a dog.  :P

Your category is too broad.  Where would I begin?  I think of all those movies on "Mystery Science Theater 3000," and it's hard to measure "worst."  Furthermore, Ed Wood movies are sooooo bad, they end shine in their cult status with a favorable light.
:D

There's a nasty little exploitation film titled "Maniac."  It was directed by Dwain Esper and came out in the mid-30s.  Today it's a party film, a la "Reefer Madness," that is so bad it's fun.

I'm not much of a fan of Shirley Temple's either, but she was the top actress for a few years in the thirties.  
If we want to go over-valued or over-rated instead of "worst," I'll chime in on "Gone With the Wind."  I've seen it in one sitting, once, and was extremely underwhelmed.  It must have been visually stunning for folks sixties years ago.  
"Casablanca" is another movie that doesn't do it for me.  Bogart, in my opinion, is the most over-rated actor in history.  Ingrid Bergman is stiff and cold as Ilsa.  There are racist undertones that really date it.  It's an okay movie, a good movie, but one of the top ten of all times?  No way.

I have to agree

"Gone With The Wind" bores me to tears

:o