Are all of those words used? How does the meaning of the sentence change when either one is used instead of the others?
1.I was disappointed with/by my result.
2.I am disappointed with/by/in you/him/her.
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The difference between "in", "by", and "with" in this context actually depends on the nature or type of disappointment you feel:
"Disappointed with" implies that the cause of the disappointment was something basic about the nature or attributes of the thing:
I was disappointed with my new toaster. It really didn't toast the bread as well as I hoped.
The "with" form is usually used with inanimate objects (like toasters), though can sometimes be used for people if you're expressing a general disappointment about their qualifications/abilities/etc, rather than being disappointed by any specific thing that they've done:
I was disappointed with the second candidate. He didn't really have the skills we need for the job.
On the other hand, "disappointed by" usually indicates that somebody has done something specific to cause you to be disappointed:
I was disappointed by Fred. He said he'd give me a ride, but he never showed up!
(The "by" form is occasionally used with objects, but most of the time only makes sense for people.)
"Disappointed in" usually indicates a deeper level of disappointment with the nature of somebody or something, or repeated problems with them, and often indicates that the speaker has lost faith in someone's ability to do what's expected of them:
I'm very disappointed in Bill. I thought he had experience with this job, but every time he does it he does something wrong.
I'm disappointed in the government. They just can't seem to get anything done!
Thus, for OP's first example context, "I was disappointed by my result" is the most common form. There's nothing wrong with with there, but in is unlikely.
In OP's second example, the most common form is "I am disappointed in you". There's nothing inherently "wrong" with either with or by - they're just not so common.
Not all native speakers will necessarily agree with me here, but I feel the above usage tendencies can lead to a potential distinction...
Apart from the obvious difference in prevalence, I think there's also a case for saying that #1 there tends to imply everything about you disappoints me, whereas #2 and #3 carry a stronger implication of being disappointed by some specific thing you did.
Normal usage is as follows:
Disappointed with (object) - an object of neutral gender. E.g: I am disappointed with your service.
Disappointed over - an incidence.
Disappointed in/with - very similar but slightly different connotation. 'In' is more personal and conveys reflection on the individual. 'With' is more used for disappointment over an isolated incidence.