Which is the right preposition: to be disappointed with or by?
Disappointed with means that you experienced something and you weren't happy with it, or it didn't live up to your expectations.
Disappointed by usually means that you feel that someone or something let you down personally.
I can see the arrow implications of the difference between: "I am disappointed by/with/in ..." and "I was disappointed by/with/in ..."Raymott
In most cases, as in the example I gave with the 'meal' sentence, the sense is essentially the same but I maintain that there is a subtle difference. 'Disappointed by' suggests something has happened that has dashed your hopes or expectations (in time line terms, a favourite of English teachers, it would be indicated by a vertical arrow); 'disappointed in/with' implies that you are in a state of disappointment because of something that has happened (in time line terms, a continous horizontal arrow). In practice, almost the same but with a different emphasis. Otherwise, they would be interchangeable in all cases, which they aren't.
'I was disappointed by him' - he let me down (one instance)
"I was disappointed by him yet again." Is this possible?
I was disappointed in/with him' - no suggestion of an action causing disappointment;
Well, something made you disappointed in/with him. It's true that you could be disappointed in him because you wanted a girl and you got a boy - which was no action on his part. But 'in/with' are just as valid if there has been an action by him.
instead, this conveys a general feeling of disappointment.
If you have a general feeling of disappointment, why attribute it to him using 'in/with'? You'd only do this if the disappointment was caused by him - in which case, you would have been disappointed by him.