The creature touched becomes less credible to people they encounter, gaining a -20 penalty to Bluff checks made to convince others of the truth of their words, even when they're speaking the truth. This bonus doesn't apply to other uses of the Bluff skill, such as feinting in combat, creating a diversion to hide, or communicating a hidden message via innuendo.
The target under the effect of glibness or similar effect must succeed at a caster level check (1d20 + caster level) against a DC of 15 + your caster level. On success, the effects cancel each other out.
Unbelievability counters and dispels Credibility.