Worst meme is probably the alt right.

IDK if it's the best meme, but one of my favorites is the Maoist Campaign Against the Landlords copypasta. Wikipedia has since edited the page on that topic to be a lot more negative and remove the reference that got copied everywhere, but I will never forget that it was the largest and most comprehensive proletarian revolution in history, and led to almost totally equal redistribution of land among the peasantry