PET BUNNIES: It could be Hugh Hefner’s upcoming 85th birthday, Robert Duffy’s fascination with the Hef or maybe Valentine’s Day. Maybe it’s all of the above, but whatever the reason, Marc Jacobs is giving shoppers at his Marc by Marc Jacobs boutique at 403 Bleecker Street quite a titillating treat this fashion week. From today through Feb. 18, two real Playboy bunnies will be a part of a Playboy-themed window display. The decor is inspired by “Hugh Hefner’s Playboy, 6 Volumes,” the limited edition book available across the street at Bookmarc, and customers can have their photos taken with the bunnies, who are wearing original bunny costumes from the Playboy vault. Jacobs also created three, $35 Marc Jacobs + Playboy T-shirts, which are available at the store with all proceeds going to Designers Against AIDS.