Stuck in the craw of the grammar police:
Unique - One of a kind, so it's not "very unique," or "most unique." It's unique. Period.
Irregardless - Double negative. The dictionary claims it is a word, but it should not be used. Amen. Just say regardless.
Could care less - Aaaargh. This has crept into the language. Should be "couldn't care less." If you could care less then what's the point of saying it?
Nuclear - People hear this mispronounced as "new-cue-lar", so they follow suit. What could be simpler to pronounce? Nu=new, clear=clear. It doesn't help that the leader of our nation always mispronounces it.
Got beat - Common error by sportscasters and those who would listen to them too much. A team or individual "was beaten," or the Illini were beaten.
It's and Its - Common error in writing is putting an apostrophe for the possessive, which is wrong. Correct - "The buffalo drank its fill." Apostrophe is inserted only for "it is." "It's a nice day."
From the sheriff's file of infrequently used words: Clowder. No, not a short version of clam chowder, but . . . a group of cats. Fancy that.