No doubt the poker wave has swept the nation, with everyone from Ben Affleck to "The Unabomber" taking a seat at the table. It finally penetrated into advertising circles when last month, Blue Rock Editorial sponsored an agency tournament attended by 50 industry players from 10 shops. Presided over by professional dealers and even a pit boss, after three hours the pool narrowed to two sharks, Y&R/N.Y. copywriter Ryan Koh and McCann-Erickson/N.Y. producer Laura Geftman. Ultimately, the crown went to Koh, an admitted neophyte who says he started playing the game just a year ago. Doesn't say much for the competition, does it? "I just got a lot of lucky cards and sort of knew what I was doing," he says humbly. The win landed him some decent booty-a couple days of editing and conform time at Blue Rock, plus a $500 Amex gift certificate, which he promptly signed upon receipt. "I felt like I had gotten lucky that night, so I was probably gonna get mugged," he deadpans.