A snooty waiter might condescend to serve you dinner at a fancy restaurant, meaning that he'd consider himself far too important to carry out the mundane task of delivering your hamburger and fries.
You might have noticed that condescend contains the word descend, meaning to move down from a higher place. You can think of condescend as lowering yourself to do a task that you feel is far beneath you. Kings and queens would never condescend to do their own laundry at the palace, for example. If they even knew how to do the laundry, you can be sure they'd do it in a condescending, or superior, way to let everyone know that housework is no task for a monarch.