"I know, right????!!!"
"I could care less." (Which means the opposite of what you think it means.)
"lay" instead of "lie," as in "You lay down, and I'll get you a blanket." Lay, in the present tense, is a transitive verb and requires an object. You lay an egg. Or you lay down yesterday. But you lie down today.
Most Americans (I would guess) only speak one language. We should at least try to do a decent job of it.
I could go on indefinitely... but with respect for the forum, here is a financially relevant one:
"Retire early?! But what would you DO???" (Not a grammatical thing, but just something people say that drives me insane. There's no way I'll run out of things to do when I'm retired.)
On the other hand, I was on the receiving end of the Grammar Police not long ago when an octogenarian corrected me when I said "okay" and complained that young people today are too lazy to say two whole words: "all right," which is more correct in her mind. She was a retired English teacher. My argument was that language changes; for example, we don't all speak like Shakespeare anymore, but that doesn't make our English less correct than his. "Okay" seems perfectly acceptable to anyone under 80. Now I don't know how to decide what's grammatical ignorance and what's just me being an old fart before my time in the face of gradual changing of the language.