I agree with Andrelle about 'mock' (but not 'rib') and Chris about 'rib' (but not 'mock'). Teasing is funny, friendly and good-natured. When you tease a friend, you often include them in the joke. Mocking is denigrating and unkind. Mocking is 'mean', because when people mock others they are laughing at their expense. As Andrelle says, it often involved cruel imitation. Ribbing? Forget about it. It's extremely outdated.

In the US I don’t think “mock” is necessarily so negative any more. There is even a phrase “good-natured mocking”. “Everyone in our small town mocked your Grandmother’s thick German accent, but she was well-loved for her generosity “ I agree that “rib” is old-fashioned. “Tease” can have romantic and sexual connotations

"Rib" and "Tease" are synonyms. It means to laugh at someone but in a lighthearted and friendly manner. To mock someone means to laugh at someone in an unkind way (usually by copying how they speak or act). I hope this was helpful! :)

They are more or less synonyms and the meanings overlap. "Mock" often includes the idea of exaggerated or distorted imitation. Mockery is always cruel. The idea is to get other people to see the victim's speech or body language as being ridiculous or funny. "Teasing" often (but not always) means tormenting someone by making them think they are about to get something they want, then yanking it away at the last instant. If you happen to know the comic strip "Peanuts," by the late Charles M. Schulz, there is a running joke. Charlie Brown always wants Lucy to hold an (American) football for him so that he can kick it. She teases him by making him think she will do it. Then the yanks the ball away at the last instant. "Ribbing" or "kidding" means a friendly insult. It is sometimes a way men can express affection without danger of seeming effeminate. "Well, Sam, look at that! Darkening our door again! You just keep turning up like a bad penny!" "Yeah, Phil, good to see your ugly old face again. I assume you are still misbehaving as usual?" In the United States today, we would be more likely to say "kidding" than "ribbing." Bullies, of course, will give someone a real insult, and then lie and say they were "just kidding." "Aw, I was just kidding, lighten up, can't you take a joke?"

The same basic idea, but different connotations. "tease" is the standard word used in most common situations. "Sally! Stop teasing your brother." "mock" sounds archaic and important. "John was imprisoned for mocking the king." "rib" is old slang that was mostly used in the 1940s. Use it if you are writing about cool people in the 1940s, or old grandfathers now. "After his plane was almost shot down by the nazis, Jack expected the other pilots to rib him when he got back to the airbase." "Dagnabbit, Sally, I'm 80 years old, but if you keep ribbing your brother, I'll tell your father to spank you."