"Disappointed in" versus "disappointed with"

Solution 1:

I don't know about any official documentation on this, but it seems from usage that "disappointed with" typically precedes a demonstrative pronoun, while "disappointed in" directly precedes a subject or an article and subject:

I'm disappointed in the ruling.
I'm disappointed in Tom.

I'm disappointed with that result.
I'm disappointed with her performance.

The 'that' and 'her' are demonstrative pronouns, while 'Tom' and 'the ruling' are subjects ('the' obviously being the article).

Solution 2:

While both prepositions are correct for everything, I would tend to use disappointed in for people and disappointed with for objects or events. I'm not alone. Consider the following Google Ngram

The majority of the time, the noun following the will not be a person, whereas you always refers to a person.