Digestive Versatility (3.5e Trait)
From D&D Wiki
 Digestive Versatility [General]
While the character can eat a wider range of foods, even those of questionable freshness, the results at the other end can be disturbing.
Benefit: The character gains a +4 bonus to resisting the effects of ingested toxins, poisons, etc.
Drawback: At any time when the character makes a critical failure on any roll, there is a 1 in 6 chance that in addition to the normal effects, the character has lost control of his bowels. If the critical failure is for a save against a fear effect, the involounary defecation is automatic. Until the character gets a chance to clean himself up, he causes any humanoid who can smell standing within 10 ft. to be sickened & suffers a -4 penalty to all Charisma-linked skills. Furthermore, anyone tracking him by scent gets a +4 bonus to Survival checks.
Normal: Characters get ill effects from eating things that are bad for them, but rarely crap themselves.
Roleplaying Ideas: Sure, you can eat that steak that has been sat in the sun for the last month, but make sure the caster has access to a Cleanse spell first...