The michelada is the punch line to a joke that doesn't exist: what happens when you cross a beer with a Bloody Mary? Popular in Mexico and throughout the Southwest, the michelada is essentially a souped-up cerveza. Recipes vary, but the idea is to liven up a light (but not "lite") beer, such as a pilsner or lager, with hot sauce, lime, Worcestershire sauce, and tomato juice. Major brands have tried to cash in on the michelada's cachet with creations like the Budweiser Chelada, which combines Bud and Clamato into an eerily pink concotion. But a real michelada is sensational, blending the refreshing quality of cold beer with salt, tang, and heat. Micheladas are easy to make, but you can also order them at such Mexican eateries as Casa Romero (30 Gloucester Street, Boston, 617.536.4341), Ol� (11 Springfield Street, Cambridge, 617.492.4495), or Tu y Yo (858 Broadway, Somerville, 617.623.5411). But be warned: once you've tried one, plain old beer may no longer seem complete.