in addition to meaning more rad, this can also mean the opposite. Radder can describe a short, on the brink of being a midget girl who is very loud and obnoxious, mainly in public places. attracts attention to where attention is not wanted. Usually a Radder has heavy make up and dresses towards to 80's revival.
-Damn that Radder is obnoxious.
-Let's get up and move over to that table, so no one will look over and see us near her.