Originally Posted by TerroristCactus
You can gain infinite XP if your speech skill is high enough (with 30 you'll be ok)..
Go to Big Town (north of Vault 101). Speak with a girl named Bittercup: she should tell you about her dating exploits. After speaking with her, go into the house marked "Common House" and speak to a man, Pappy. There should be a speech skill dialogue option that says "You came here with Bittercup, right?" You will get XP every time you click it. Continue to do this and you can rack up XP in mere seconds. Bethesda has not yet patched this glitch so....RUN!!!
easy way to get silver toungued devil achivement