should of, would of, & could of; those in particullar get on my nerves especialy when ppl use them and then claim to be college students or graduates, yeah right... it's could've, should've, & would've or the words they are conjunctions of, being; could have, should have, & would have, also acceptable are the slang variants of coulda, shoulda, & woulda...
another one is irregardless, putting "ir" at the begining of "regardless" cancels out the "less" at the end of "regard" and then makes it where you should have said "in regard" or "regarding" instead, thus becoming the opposite of what was originaly intended to be said, besides irregardless isn't even a word it's not even slang...