Is this sentence correct?
It is sad to see people disrespecting the teacher.
Why wouldn’t it be?
Maybe I’m stupid…
I’d say so. After all, the sentence, “It is good to see people respecting the teacher,” is gramatically correct, and “disrespect” behaves the same, gramatically speaking, as “respect” in every other case.
That said, it does sound odd, but I simply can’t find anything wrong with it.
Are you actually asking a vocabulary question? Do you want to know whether “disrespect” is an acceptable English word? The answer is, yes, it’s in the dictionary I just checked with this meaning. If this is your question, you need to learn the difference between grammar and vocabulary.
AFAIK you sentense is correct. The usage of disrespect as a transitive verb is much more common in the USA then in the UK (according to my g/f at least!)
I’d probably say “It is sad to see people not respecting the teacher.”
It is sad to see the students giving the teacher disrespection.
President Bush, is that you?
Why y’all be disrespectin’?
FTR it appears that “to direspect” has been around for about 400 years. OTOH, it’s in the category of words I’d avoid when speaking to anal people. OTGH, I personally would recognise a shade of meaning between ‘disrespect’ and ‘no respect’ - disrespect sounds a bit more active to me.
I will provide a voice of dissent here, and say that if you are writing for a serious publication you should not use “disrespect” as a verb. As a professional editor, I would never allow it to stand in any copy I was reading.
Although I note from the OED that using “disrespect” as a transitive verb goes back to at least 1614, in my experience it has never been used that way by serious writers. In the last ten or twenty years, it’s become a relatively common “street” term (whence to “diss” someone), but it still strikes old farts like me as a barbarism.
Joe Random says that “disprespecting” is logical by analogy to “respecting,” but personally, I would avoid that construction, too.
In my opinion, “showing respect” and “showing disrespect” are preferred usages, so I’d cast the OP’s sentence as, “It’s sad to see people showing such disrespect for the teacher.”
Not logical, perhaps, and I can’t provide any cite or authority other than my own ear. It just sounds better to me.
So would using “disrespect” as a verb be along the lines of using split infinitives - not wrong but you probably should avoid it.
More or less.
It’s a matter of style rather than correctness.
In this case, a moribund verb was resurrected as “street slang” and still carries an odor of edgy, streetwise attitude. Hence, even though correct, it is advisable to avoid its use in anything more formal than a friendly letter or dialogue in a story.
(Note that the noun “disrespect” is much less redolent of the street usage than the verb. “Contemporary American culture is characterized by disrespect for established tradition” is in no way offensive, though “…by lack of respect for…” would probably be preferable unless the context implies active acts showing the D word.
I agree with Polycarp that it is largely an issue of style, but the difference between “disrespecting” and split infinitives is that the latter can be found in the works of great writers (e.g. Gene Roddenberry) and, to my knowledge, the former cannot.
The horrible trend in this country (US) to create transitive verbs out of nouns drives me insane. What’s even worse/sadder is that some of them stick.
It’s almost as if people think they sound more sophisticated when they speak using these artificial constructs.
I should start a separate thread to collect these horrors.
Appropriately enough, it’s called “verbing,” and as Calvin (of “and Hobbes”) said, “Verbing weirds language.”
I agree with you about it not being professional NOW. But can you show it never was used by serious writers? I know there are other examples of constructions Shakespeare used, then went out of fasion for 400 years, and now are coming back in, but aren’t approved yet.
Language changes, and if Kel Varnsen and other writers start using “disrespecting,” it may eventually be accepted as standard usage. (And may their souls burn in the deepest pits of hell!)
But seriously, there are those of us who can remember when “impact” was not a verb. But it’s a rare editor today who would absolutely refuse to allow it, if an author insisted. Try as we might, there’s no holding back the blind forces that change language.
Even though fighting such changes is a quixotic enterprise, it’s one of the few things I find myself passionate about. I don’t much care what people do, as long as they don’t hurt others: drugs, prostitution, putting bits of steel in your privates…who cares? But using “it’s” when you meant “its” should result in a six-month jail term!
I once worked for an ALJ who was dead against “verbing.” When I wrote “John doe opined…” he objected that “opine” is not in his dictionary. I pointed out to him that he had a 19th century dictionary in his office. He also, of course, objected to “impact” as a verb to mean “affect.” He said that nothing exploded.
IMHO “opine” serves well. To replace it with “was of the opinion” or similar jargon adds unnecessary verbiage. We have many such verbs now and they have been accepted by most everyone…with one or two exceptions. 
However, “impact” merely replaces another serviceable verb, “affect,” and serves no additional purpose. That would not be too bad except that it has been overused lately, to the detriment of “affect.”
Shouldn’t that be “more worser/saddister”?
DIS-R-E-S-P-E-C-T, find out what it be meanin’ to me…