disappointed with/in/about someone

Any of the above, but it changes the meaning. Disappointed with and in mean generally the same thing, but disappointed about makes it about a situation. "I'm disappointed in/with John" - John did something that I dont approve of "I'm disappointed about John" - something happened to John (to varying degrees of badness.) "I'm disappointed about John, they didn't have to fire him."

Disappointed in/with have the same meaning if we are talking about a person's it means that person has let you down in some way. Not live duo to your expectations of them. Disappointed about is different. Eg, you could say "I'm really disappointed about John." When talking about them having to be out of town so they can't be here. It doesn't really imply you are upset with them or expected them to do things differently. Basically "about" could have a lot more meanings depending on context because "about" allows for things around John, or things that happened to John, not just John themselves being the disappointment.

"by" might be better. "With" and "in" are acceptable. "about" is strange. You'd be disappointed about what someone *did,* but not just about them. (You probably meant "John", not "Jonh".)