are sheep for sheep and fish or fishes for fish. Sheeps is only a form of a verb. Sheeps means grazes. Yes, the plural of "whim" is boring old "whims." However,there is "cacti" and "cactuses." Even more fun is that there is "octopi," "octopuses," and "octopodes." More plurals fun: rhinoceroses, rhinoceri, rhinocerotes.
Yes, I'm afraid I also fond FGZstar's poster both meaningless and mildly offensive. [Plural] I still occasionally come across people who insist "data" can only be a plural. Funny that they don't make the same fuss about "agenda".