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A person, usually overweight & out-of-shape, that always posts on facebook when they're working out (& often exaggerates their accomplishments).
John: "Just finished 5 hours at the gym."
Brian: "You Facebook exercibitionist! You've never even looked at a gym for that long."

Matt: "Just ran a marathon in 2 hours."
Brian: "That'd be a record for someone your size, you Facebook exercibitionist."

Jen: "Off to do yoga, then on to insanity cardio & P90X."
Brian: "I know you're trying to attract a man, but don't be a Facebook exercibitionist."
by Johnny Drama Johnson August 17, 2011