So-and-so and Somebody

So-and-so noun - A person whose behavior is offensive to others.

Somebody and so-and-so are semantically related In some cases you can use "Somebody" instead a noun phrase "So-and-so".

Somebody noun - A person who is widely known and usually much talked about.

So-and-so and somebody are semantically related in importance topic. Sometimes you can use "So-and-so" instead a noun "Somebody".