forum jockey
a person who posts online in a manner to make themselves impressive and is often caught up in his/her own lie by other online posters
posterA: i raced a ferrari on main street with my car last night and kicked its butt.
posterB: main street has been shut for a week.
posterC: haha, what a forum jockey
posterB: main street has been shut for a week.
posterC: haha, what a forum jockey