Chaotic Stupid (3.5e Flaw)
From D&D Wiki
You do whatever you want. Whatever.
Prerequisite: Non-lawful alignment
Effect: Whenever you would make a decision, roll a Will save with DC equal to 18 minus your Wisdom modifier. On a failure, you must act in a way that the Dungeon Master dictates.
Roleplaying Ideas: Dungeon Masters, slap this flaw on any player who acts with no logical course of action.