The fallacy of inconsistent premises (or simply, inconsistency) occurs when an arguer uses a premise that contradicts another premise used earlier by the arguer.

Here is an example:

Sal and Ahmed are ordering at their favorite fast food restaurant.

Ahmed: "Why do you always order chicken nuggets at this place?"

Sal: "Because they taste yummy."

Ahmed: "Then why don't you ever order the chicken sandwich?"

Sal: "Because I'm vegetarian."

Ahmed: "Ummm, wait...."

Ahmed is right to be perplexed, because eating chicken nuggets is logically incompatible with being vegetarian.