this is someone who looks ike squidward. This is an insult and can be used at anyone. Squilliam williams typically swallow and they are often seen as jewish people. It is not exclusive to jewish people as it can be used to any religon. They also normally have a bowl haircut and are mda hot though. the term can also be switched and people can be called a william squilliam.
bro john is such a squilliam william.