Let's begin today's class with irregardless. Okay, technically it is a word but it is an illogical one. The prefix ir means 'not' and the suffix less means 'without' therefore creating a double negative within the word (thank you Wikipedia!). Now I may have spent my formative years down south but even I know double negatives are a no-no. I'd like to take this opportunity to declare that y'all and ain't are words no matter what a yankee might believe.
When expressing your lack of emotion over something please say I couldn't care less rather than I could care less. I could care less is saying that you do, in fact, care. That little n't contraction is very important in this scenario.
Let's move on to writing, shall we? There are enormous differences in the meanings of the words their, there, and they're. Same with you're and your. And with through and threw.