A friend with whom you hang out with only to better your personal image. An accessory friend is often mean, snotty and disliked by the entire friend group. The only reason the accessory friend is tolerated is because of their above average looks.
Bob: "Nicole, why do you hang out with Barb? I'm pretty sure that my antisocial cat has a better personality than her".
Nicole: "Good question! Barb is just my accessory friend. I only hang out with her because she makes me look good... kind of like these diamond earrings that I'm wearing.
a living being used as a fashion accessory, like a handbag or a scarf, except that it's alive; often dressed up in cutesy little outfits
Paris Hilton rarely goes out without her bio-accessory, Tinkerbell the Chihuahua. Britney Spears used to carry around her bio-accessory, Bit Bit, until she started carrying around babies instead. Why didn't Kevin carry the dog? Maybe that's why she divorced him: he wouldn't carry the little dog.
A term recently awarded "The Most Outrageous Word" by the American Dialectical Society, referring to Angelina Jolie's adopted Cambodian son. The term suggests a cynical motive for celebrities adopting children from third-world nations, being more to promote their public image than from any genuine motive of saving starving children.