It really depends on the context, but in every case it is very informal. You can't just use it as a synonym for "girl" or "lady". If you use it in the wrong situation, it could be rude. I've heard it used in these situations. 1. Men (guys/boys) use it to talk ABOUT a woman. "That's a hot chick." 2. A man or woman might use it in a derogatory way. "I'm sorry I'm late; some chick was holding up the line at the grocery store." 3. People don't use it to talk TO (address) a woman. If you do, it would probably be in a mean way. "Listen, chick, move your car now or I'll call the police."

It is not rude. It is just sometimes inappropriate.

Think of little, fluffy chickens with a tiny brain. Would you like to be called one?

It's `just a slang. It's not rude. You can say, "hey chic, how are you" It's very common in English terms, but not standard English. "Have a great day chic" is another example. When you say it to the girl, make sure to smile... :-)

Don't use it if you want to speak formally, but otherwise it's relatively common. If a man is using it to refer to a woman, he's probably being impolite, though.