I was just thinking about RENFE, the Spanish rail network; RENFE stands for REd Nacional de Ferrocarriles Españoles. I always thought the joke that it stands for Rogamos Empujar Nuestros Ferrocarriles Estropeados (Please Push Our Broken-down Trains) was hilarious. These ironic acronyms go back a couple hundred years at least, and exist in English as well; at the time of the War of 1812, the United States Light Dragoons (that is, the cavalry) had USLD on their saddlebags; the joke was that it stood for "Uncle Sam's Lazy Dogs."
In addition, in English normal words can be turned into humorous acronyms, which I've never heard done in Spanish. FORD supposedly stands for "Found On Road Dead" and ADIDAS stands for "All Day I Dream About Sex." Fake acronyms are often invented to explain the etymology of a word; popular (and false) wisdom holds that TIP is "To Insure Promptness," FUCK is "For Unlawful Carnal Knowledge," and "POSH" is "Port Out, Starboard Home."
Can anyone think of any other examples?