Steal, steal, steal. But make sure you are crouched and it says [HIDDEN]. Kill good characters. Most of all blow up the bomb in Megaton. Help the ghouls take over Tenpenny Tower. Become a slaver at Paradise Falls.
You Can also use speech to do evil deeds like when the goul asks for scrap metal in underworld you can do a speech check to threaten him to give you all the stimpacks for a loss in karma