You must have a speech skill of at least 30 for this cheat to work.

Find the "Big Town". Once you're there, go to the house just left of the bridge.

Inside that house there will be a girl named "Bittercup". Talk to her and find out that she had dated a man named Papy (I think it's Papy).

She can also be found sneaking around Big Town at night.

After you do this, go find Papy, and talk to him.

You should see a speech challenge choice while talking to him.

Keep doing this challenge ( it may not work the first few times.)

The speech challenge never goes away, allowing you to keep doing it over and over, and getting unlimited XP.