Here are some words people use incorrectly.
Unthaw: You can’t unthaw something. Well, you could, but there’s a better word for it: freeze.
Irregardless: Do you really need this one explained? It isn’t even a word.
Nauseous: You probably mean nauseated, unless you’re barfing in front of other people. Then you should just go ahead and say “naushous” and wear tighter trousers.
Lay: You can’t lay down. You can lay something down. But you can’t, yourself, lay down. You lie down.
Ironic: Most people are better off just not even trying to use this word.
Pristine: It doesn’t mean ‘clean’. It means ‘in its original state.’ There are parts of the Amazon that are filthy, muddy shitholes filled with bugs and snakes, and they are pristine.
Enormity: When someone says ‘You’re failing to grasp the enormity of the situation,’ he’s not saying something is really huge. He’s saying it’s really evil and terrible. The holocaust was an enormity. 9/11 was an enormity. An expensive wedding is not an enormity. Well, maybe not at the time, but just you wait.
Nation: You probably use ‘nation’ and ‘country’ interchangeably. But you shouldn’t. A country is a geopolitical entity. A nation is its people. “We the people of this great nation” doesn’t mean “we who live on this particular section of land.” it means “we who are linked by citizenship.”
Check my links down there to the right for a good general usage page I always find helpful.