Prostitutes have long claimed the title for the world's oldest profession, but we're guessing the lusty ladies must have been neck-and-neck with the burly dudes who beat copper into knives and other tools. There's still something very blast-from-the-past about paying a visit to Saucy Joe, an itinerant merchant who parks his mobile knife-sharpening truck around the city like a Renaissance-era peddler. He will sharpen anything from a pocket knife ($5 if it's under 4 inches) to a meat grinder ($15) to an ax (price to be determined). Still, he has tooled his trade for 21st-century San Franciscans: He reveals his ambulatory location on his website, and updates with constant tweets — just follow @SaucyJoe.