Marx Brothers/YMMV


 * Acceptable Targets: A little person is mocked and threatened in At The Circus. It works because it makes Groucho seem cowardly and weak instead of cruel.
 * Upper class people don't generally come up with the longer end of the stick either. But then again, few people get treated well by the characters the Marxes play.
 * Of course, a lot of that comes from the Depression Era roots of the act; The Three Stooges and other comedy troupes of the time did the same.
 * Once-Acceptable Targets: "Then the Headstrongs married the Armstrongs, and that's how Darkies were born" -- Groucho in Duck Soup. Also, Chico's portrayal of an Italian immigrant, Harpo's original "Irish bruiser" character from his vaudeville days, etc. Hey, it was the '30s!
 * The "that's how Darkies were born" thing was actually a pop-culture reference: it was a play on an incredibly racist song that was popular at the time, "That's Why Darkies Were Born": the lyrics of which basically said "someone had to be slaves and have crappy lives -- so it's you" It could be read that Groucho-- himself a Jew, and probably quite familiar with racism-- was ridiculing the warped logic of the song.
 * Of course then there's the scene in The Big Store where they have black actors literally picking their cotton in-store...