Portlandia returns for its fourth season February 27, but in the meantime, they have a goofy web series about tailgating for “Prairie Home Companion.” (It’s also a car commercial masquerading as a Portlandia sketch, so don’t be too surprised when, for no reason, talk turns to the wonderful features of a car.) The sketches are everything the show does well, namely ultraspecific gentle mocking of the tote-bag crowd. How does one tailgate for “Prairie Home Companion”? The same way one does everything on Portlandia: With yerba mate, slow-cooked soup, tales of Peter Segal, surprisingly good wigs, background actors who seem very amused to be on the show, and terrible middle-aged-white-guy dancing. NPR jokes! Let the fun never end.