By definition, "patronizing" is displaying or indicative of an offensively condescending manner. This word is often used to describe someone who uses sarcasm or gives a back-handed compliment to another person.
Synonyms of "patronizing" include to treat condescendingly, to look down on, to talk down to and to treat with disdain. A person who is acting in a patronizing manner often feels superior to the person to whom he is speaking. A patronizing person may also talk to another person as if he were a child, speaking to him in an overly simplistic manner to try and get a point across.