Compulsive Killer (3.5e Flaw)
From D&D Wiki
When somebody pisses you off, they are going to die before the night is done.
Effect: If anybody angers you (for example, harms an ally or directly opposes your ideals. This could be something defined in your character's background story, if one such exists, or because of opposing alignments), you must make a will Save (DC 15 + 1 per HD) in order to avoid killing the person that angered you.