"Disappointed in".
It just doesn't make any sense. Sure you can be disappointed with someone or something, but being "disappointed in" it has too many non-figurative shades of meaning to be a good substitute. You might as well go the whole hog and use any arbitrary short word in its place, it would mean about as much. "Matthew, I've just been told your grades are atrocious. I'm disappointed of you." Also, as Flann O'Brien, a keen observer of linguistic absurdity, typed back in 1940-ish:

"I often wonder am I... mad? Do I take that rather Irish thing, O'Fence, too easily? I go into a house, for instance. My 'host' says 'sit down'. Now why down? Why must he be so cautious and explicit. Is there not a clear suggestion there that if he had neglected to be precise, he might turn round to find me seated on top of the bookcase, the head bent to avoid the ceiling and the air thick with fractured cobwebs? How equally stupid the phrase 'stand up!' And how mysterious the sit-down fight as opposed to the stand-up fight!"

I'm a real hit at parties by the way.
( The Mock TurtIe ™ --- Thinks you are a cunt, on, Tue 13 Apr 2010, 22:39, 1 reply)

Dont be an arse!
Skim / skim, but would anyone sit on a bookcase? Don't be daft but respect the social requirements.

If you spawn then you will do the same. If you have, then tie the fuckers down!

And
(Suck it and Sea, Tue 13 Apr 2010, 23:03, closed)