To 'patronize someone' or 'to be patronizing' is more less speaking down to a person usually in a 'sweet' manner (i.e. subtly acting like you're better than them, acting in an arrogant manner, treating someone like a child) but not opening being hostile or mean. Think of a person talking to you sweetly, but it comes across that they are superior to you, don't respect you, don't take you seriously, etc....then they would be 'patronizing towards you.' It comes from back in the day when artists and writers were literally patronized by rich, wealthy people....i.e. wealth people ( the patrons) gave money to artists to support their work or more often to commission work that was meant to bring glory to the wealthy person. I could imagine, in this situation, it could be annoying for the artist because they were completely dependent on the wealthy person for money and support-- this would create a dynamic we're the wealthy person, probably with a big ego,  had all the control and could abuse or take advantage of the artist emotionally because of their dependence on the patron.

Thank you everyone. It seems like you are saying that patronizing is to be condescending towards someone. But I think there is more to patronizing. I can't grasp it. How do I recognize when someone is patronizing? I can easy detect when someone is condescending. I do understand to be a patron of a store, etc.

Typically if you are patronizing *someone*, it means to be condescending toward that person, in other words, "talk to someone in a way that implies they are less competent than they actually are". If you patronize a *business* (like a store, for example) then it just mean to be a supporter of the business and shop there frequently.

A "patron" is a client. (example: I am a patron of that store.) To "patronize" someone or something is to act as a client. (ex: I patronize that store.) By extension, "patron" and "patronize" refer to offering support. (ex: I patronize that artist, or that charity). From the unfortunate notion that someone who accepts help is somehow inferior springs the connotation that turns patronizing into a sort of humbling. In this interpretation, "patronizing" someone means regarding them as if they were begging for help from you or, in other words, looking down on them.

It can also means to support someone financially, typically an artist.