My assistant stood up to me today. She said I should sit on the other part of the sofa when I wanted to take a nap where she was. If you stand up to someone, it means you tell them you won’t do what they want, usually because of a principle. Humans should stand up to their bosses more often, but never to their cats. If you stand up for someone or something, it means you support them, and like with stand up to, there is usually a principle or an important reason. If you’re a “stand up” type of person, it means you’re realiable and loyal.
If you’re a stand-up comedian, it means you go places and tell jokes for a living. Sometimes these people tell jokes about cats.