An example of how uncorrected grammar enters the mainstream is the expression "try and ..'
For example, one cannot try and eat something. It is an anomaly. One either does or does not eat. The correct and logical English wording should be try TO eat.
Without correction, this error has infested society.
Another error that is spreading like a plague is the use of the word of instead of the abbreviation 've. For example, could of instead of the correct could've.

Depends on how it is done.
Remember, if no-one corrects grammar it becomes accepted as correct by others and leads to a deterioration of the language along with a devaluation of education.
A stitch in time ......

Depends on how it's done. One can try and use the same conversation but with the correct grammar. Let the other hear it again differently and they may either think you are wrong or it may even plant a seed. People seldom respond to force so tact is often needed.

It probably is rude.

I agree...it is sorely tempting to feel the need to correct bad grammar, but it’s an urge we should resist, unless it’s our own children. Just look on it as an idiosyncrasy of your dad’s ...an endearing, if irritating, quality! Your ex was completely out of order in my opinion...it is not an endearing quality to correct other people publicly, quite the reverse in fact!

It's a fine line. Ordinarily, I don't correct people unless in private and I know they're receptive to correction. I want to know when I make mistakes, and I try to gently extend the same courtesy. I'll tease my father about grammar mistakes he continually makes, but he's good natured about it and it's sort of an inside joke between us. To his credit, he's improved his grammar, pronunciation, word usage, etc., over the years and does care about how he comes across to others.

There was only once when I corrected someone in public, and it was only because a colleague had made the same mistake repeatedly in a lunch setting and I was feeling uncomfortable on his behalf. I tried to lower my voice so I didn't draw attention to his mispronunciation, but he was clearly annoyed that I'd said anything. I tried to smooth it over by letting him know that I knew the correct pronunciation only because of the name of a local spot with that word in it, but when I said, "I only know that word because…" he cut me off so everyone at our table could hear and said, "… because some asshole corrected you?"

So, I will never again correct anyone in public even if I know they're embarrassing themselves and I'm attempting to be discreet. It's really none of my business anyway, and there's no foolproof way to do it gracefully and inoffensively.

Mostly I don't
.but on that rare occasion the misspelling, had to have just fucked up the entire sentence.

I just cringe about it in private.....

Driving in Georgia, I made fun of misspelled signs until my sister told me to shut up.

As a volunteer college mentor, I correct spelling and grammar mistakes in student essays.

I would never humiliate someone in public.

On a first date, a jackass repeatedly corrected my pronunciation. Each time, I looked it up. Not only was he rude, he was wrong. As a lawyer, he kept arguing. Flush.

OMG I don’t say anything about someone’s grammar but it’s like finger nails on a chalkboard.
Along with infantile slang like “on” accident. I want to body slam them head first into the pavement it’s “by” accident people!
When I die it’ll be from a heart attack because some stupid prick did something on fucking accident.
I’ve never said that before, to anyone, it felt good
I like this place, it’s cheaper than remote therapy.

Aside of correcting one's own children, yes, it is rude to correct another's grammar - but sometimes bad grammar can be infuriating! I understand the urge to offer correction!

There is a polite way to correct another adult, if done carefully. One could simply work the correct grammar into one's own speech, hoping that the offender will take note of the correct usage. Alternatively, one could say, as though surprised, "Oh, is that how it's said? I always thought it was (correct pronunciation or phrasing)."

Of course there are exceptions to this rule! I have a dear friend who, as old friends do, enjoys ribbing me by deliberately using simply atrocious grammar and pronunciation. Since it is clear that we are just sparring, I feel quite free to correct him loudly and passionately, even knowing that this will only encourage further transgression.

I only correct grammar when I want to be rude. If someone corrects me I assume they are trying to be an asshole.

I'm a total grammar nazi, but I keep it mostly to myself and those I know would appreciate the better understanding or improved quality of a written statement.

It is really appropriate only in the context of a teacher/student or an adult/child relationship. For that reason, when employed between equals, it is only a power play, or at best, mindless rudeness.

It’s kind of a dick move to make yourself feel better when that is your only argument to their reply, but it says more about you than them.
I actually enjoy seeing it.

If it is for better understanding then it could be for proper clarification of the information transfered.