Sauce béarnaise syndrome is the official name for the learned taste aversion to a food that comes after that food has been associated with nausea, even if you are intellectually aware that the food was not the cause of the sickness. It was named by a psychologist, Martin Seligman, who happened to have steak with béarnaise sauce the night he got violently ill. Though he later found out his entire workplace had been subject to stomach flu around that time, he still could not stand the thought of béarnaise sauce for the next ten years. His colleague John Garcia had been experimenting on radiation sickness in rats and reported that sick rats not only rejected their "rat chow" while they were ill, but after they recovered. Seligman was fascinated by the similarity of human and rat behavior and coined the name. It's been found in many other animals, even slugs. However, the behavior was slow to be recognized because it breaks the rules of operant conditioning; the food and the sickness can be hours apart instead of the brief period that is felt to be necessary for conditioning. (Garcia was shunned by the psychological community for his unacceptable finding and committed suicide.)

Evolutionary biologists theorize that this phenomenon spreads because organisms who eat something toxic, survive, and then avoid that item in the future are less likely to die of poisoning than those who don't avoid it, and dead organisms don't reproduce. (And some animals take advantage of the aversion -- the monarch butterfly eats the bitter-tasting milkweek plant and is unpleasant for birds to eat. So birds avoid not only monarchs, but other species of butterfly such as the viceroy that have similar bright orange, white and black coloring.) The phenomenon also interests neurologists because of its power to make an impression on the neurons of the brain with a single instance. The reverse of the syndrome also happens; people and animals who feel better after eating a food will continue to like that food even if that food has no real connection to their recovery.

The phenomenon has been manipulated for medical purposes -- children who get nausea-inducing chemotherapy drugs often don't want to eat their usual foods since they associate them with the sick feeling. Dr. Ilene Bernstein of the University of Washington has tried giving these kids unusual flavors of ice cream before chemotherapy, so that the aversion will be attached to that flavor instead of their everyday food.

Sources:
Nesse, Randolph M., and George C. Williams. Why We Get Sick: The New Science of Darwinian Medicine. New York: Random House, 1994.
http://www.salon.com/health/feature/1999/04/28/taste_aversion/
http://www.bsi.vt.edu/bklein/vnbhm/Announce.html