Bullies know exactly the people who would not hesitate to speak up against them and question their actions. They know that it is extremely difficult to dominate them and hence choose a different way to intimidate them. They crack jokes on them in a public setting to offend them and belittle them.
The jokes are intended to hurt the other person and make them feel bad about themselves. They are humiliated in a public setting and that makes it even worse. It is imperative that employers protect employees from bullies and foster a team environment at the workplace.