Context, as always, is king.

American English has no language college; there's no formal keeper of the flame like there is for Latin or Spanish. That allows the language to flow but it also masks certain developments. Thai, for example, has five registers - Street, Formal, Rhetorical, Religious and Royal. There are rules of grammar and diction for each. They basically codify that when you're writing a legal brief, you're going to use different grammar, diction and syntax than when you're buying a durian off a street vendor. We do the same here, of course - but we don't have any rules or guidelines that say "it's okay to do this in this setting but not that one."

There are rules for "street American" and they are very different than for "formal American" but since they aren't published anywhere, and since there's no agreement, all we know is that we're all taught "formal American" and that we get in trouble with our teachers with "street American" but if we use "formal American" on the street we get in trouble with our friends. It's a confusing situation.

Local news anchors have been screwing stuff up forever. You can generally tell how many copy editors have been over something by the correctness of the grammar. I start every morning with the Daily Beast's Cheat Sheet and I'm pretty sure I've done more proofreading of this post than they do of the entire page. It has to be a conscious choice on their part.

I once worked on a commercial where the tagline was gramatically incorrect. We'd shot it all day. I'd captured an hour of audio of it. And then the agency kept me late for no reason because they couldn't get their shit together. It was one of those gigs where the Agency gets a Starbuck's truck but crew gets Subway Tuna... you know what I mean?

So I waited until the 2nd hour of overtime as we were capturing wilds and mentioned "that's a split infinitive, by the way."

The bitch's eyes went big and she stuttered. I have no idea how badly I fucked her night, but I hope really badly.

Slightly related note: In defense of "like"