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.
To be more Radical
I'm way radder than you're sorry ass, chump.