Someone who logs onto Facebook for a very short period of time to look at all of the updates on his or her feed, check for wall posts and messages, and update his or her status. This sniper then logs off as quickly as possible to avoid being caught in conversation with Facebook campers. This is a way of life for people who dislike Facebook chat or have "friends" who like it way too much to be healthy.
Her Facebook sniper routine has been streamlined to about thirty seconds, ninety if her friends have been up to anything interesting or if she feels the need to reply to something. She prepares her status updates beforehand.
That one guy/girl who you barely know (maybe you had one class with them, in middle school, and you don't remember them ever saying anything to you, and you only ever heard them speak...once) you accepted a friends request from them and then they randomly comment on an update that you post on your facebook even though you never actually talk to them.
Whoah, that kid with the crutch in Physical Science Freshman year just Facebook Sniper'd me!"