-Infrequent or nonexistent use of capital letters and/or punctuation.
-Bizarre behavior and use of the English language, which is often described as either ghetto, otaku, forum female, fanboy, or even l33t d00d, or a combination of the above.
-Avatar consisting of an anime or video game character, animated sprites from Metal Slug or Final Fantasy, or the forum default Homer Simpson picture.
-Username consisting of at least five numbers or underscores.
-Huge, ugly Photoshop abortion of a signature which may stretch the page frames.
-Terrible or nonexistent lack of personality
-Completely worthless, typical, or irrelevant opinion on anything.
Most forum rats are preteen kids, and often either a fanboy, wigger, jock. Though they come and go, no board is safe from them unless the admin only lets his/her friends register.
Forum Rat: "Pics or fake."