To clarify my comments about Mexican food...

First off, the rule actually applies to all ethnic restaurants, not just Mexican.

Stated in a nutshell, the rule is "No matter what you order at an ethnic restaurant, someone at another table will have ordered something that, when it's served, will make you wish you had ordered it instead."

Ironically, if you ask the waiter what that person ordered and order it next time, someone else will have ordered something else that will make you wish you had ordered it instead. It doesn't matter what you order, what someone else ordered will always look more interesting. Of course, there is some comfort in the fact that what you ordered will always look more interesting to someone else than what they ordered. It's a never-ending cycle.

It probably has to do with the fact that while you're waiting for your food to arrive, your food exists only as an abstraction, while the food of the person who's actually being served exists in reality and is, therefore, more immediately desirable than what you ordered. Or is that too Platonic of an explanation?