Someone who spends the majority of their days and nights Facebook stalking/creeping their family and friends. A true "Guyeski" is in his/her prime stalking hours late at night when the rest of the world is sleeping, or very early in the morning, getting their Facebook "fix" before they start their day. Facebook users should NEVER leave their statuses unattended for very long, for fear that a "Guyeski" will "like" it. Sometimes, "Guyeski's" are referred to as "BG's".
Did you see what Molly did on Facebook yesterday? She "liked" 37 of her friends statuses. That's got to be some kind of record. She really went "Guyeski" on the Facebook community.