The adjective demeaning describes something that lowers a person's reputation or dignity. If your boss always asks you to pick up her dry cleaning and get her coffee, you might feel like you usually get the demeaning jobs.
The adjective demeaning comes from the verb demean, which itself is based on the construction of the word "debase." The word demean has two almost opposite meanings, to degrade and to conduct oneself in a particular manner, usually a proper one. The adjective, however, always describes something that is degrading. Overhearing two friends gossiping about you can be a demeaning experience, even if they're just criticizing your new haircut.