Is it ever not considered rude to correct someone's grammar and spelling? Not in a business setting or anything, but will I come off as a dick for pointing out mistakes in an an e-mail, chat, or Facebook comment? Some of my friends type like fifth graders, and it's highly annoying.
I can think of very few situations where correcting someone's grammar would ever go over well. Those situations include: It is your child/student you are correcting, a co-worker with whom you are working on a presentation, or if you are actually discussing grammar when someone makes a grammar faux pas. Then you may chastise him/her, a right guaranteed by several constitutional amendments, I'm pretty sure.
Otherwise, save it. Chances are they probably noticed the mistake. If you can reasonably tell what it is they meant, then keep your trap shut. If they're, like, constantly using the wrong to/two/too homonym, it's unlikely that an online scolding will do anything to change that. Also, embarrassing someone in a public forum over something frivolous is just bad form. If you absolutely must say something, then you better make it funny or cute. A friend recently pointed out a typo I'd made in a Facebook status: "I
was really laid into this girl in my column" by asking if I'd made a Freudian slip. That's fine. If he had said, "Anna, that's wrong. There shouldn't be a 'was' there. Look how wrong you are" that wouldn't have gone over as well, see?
If you're trying to correct a friend's excessive LOL usage or Teenglish text vernacular, that's even more of a lost cause. I know plenty of highly educated people who chat and text like they just drank a whole barrel of Grapes of Wrath-era moonshine. I've had bosses who winky face everything, making all correspondences about Excel spreadsheets seem faintly suggestive. "This looks great, but what about if we inserted another column? ;)" This is just something I've grown to accept or ignore, depending.
Even if it weren't rude, which it is, it's hardly ever worth the time or effort to comment on grammatical, typographical, or orthographical errors. We all make mistakes. Yes, even you, Sir Lance-But-Never-Alot. It'd be one thing if said mistake was some unspeakable evil haranguing mankind, like Snooki or jorts. But it's not. It's a comma splice. Casual correspondences like texts, e-mails, blogs, chats, and so on, are seldom subject to proofreading (Caveat: Online daters of the world, please proofread your messages! It will get you laid!). If you want to be "charitable" then go donate money to a cause instead of wasting your hard earned "generosity" on those who won't appreciate it. I will say this, though, if a friend expresses confusion or doubt about a grammar or spelling-related foible, and you know the answer, then by all means, Schoolhouse Rock their world.
A little more slack can also be given to pronunciation problems. For instance, I'd been saying author Annie Proulx's name wrong for about 80 years until someone finally chimed in and told me it was pronounced Proo, not Prowlex. Again, do so in private, but if a simple correction will save a friend from feeling like a piss-ass forever more, then you can take them off to the side and say something like, "Actually, Anna, it's Marcel Proost, not Prowst. Those wacky French, amiright? They add 17 extra letters to a word and it still ends up sounding like ooh. Also, clearly you should never say anyone's name that starts with Pro."
The only other time you're allowed to go all comma sutra on someone's ass is if it will delight the whole Internet. Witness:Social-media mistress Anna Pulley likes to give advice about how to play well with others on the internets. If you have a question about etiquette involving technology, shoot her a question at AskAnnaSF@gmail.com.