Picture Dean Martin swilling a martini or Bill Murray playing Nick the Lounge Singer on “Saturday Night Live,” and you get an idea of Lee Diamond’s schtick. Better yet, skulk into the dimly lit Back Door Lounge in Old Sac on a weekend night to catch the dark-haired Diamond crooning “Fly Me to the Moon,” “That’s Life” or some other golden oldie, accompanied by a prerecorded backing track, karaoke style. “I take requests, but I don’t do songs I don’t like,” says Diamond (real name: Gaetano LaMotta), who marks his four-year anniversary at the lounge on Dec. 5. His wildest request? “Over the Rainbow,” which he sang a cappella when a customer offered $100. “A hundred dollars changes a lot of things,” Diamond quips. The guy’s got a wry sense of humor—his MySpace page says he’s 101 years old—and a multigenerational mix of fans—“from 21 to 81,” as he puts it. It’s true: The last time I caught Diamond’s gig, I spied some hip 20-somethings getting misty-eyed as they watched a gray-haired pair dancing cheek to cheek. See for yourself at the Back Door Lounge, 1112 Firehouse Alley in Old Sacramento, where Diamond performs Friday and Saturdays from 9:30 p.m. to 1 a.m. No cover. For more information, call the lounge at (916) 442-5751.