Inc.com recently listed 10 improper (but common) phrases that can make you look bad. Of the list, I think that 5 are particularly common:
Must of, should of, would of, and could of
All those "of"s should be "have." As one reader points out, the proper versions were corrupted by contractions such as "must've."
Worse comes to worse
Another reader points out this should be "when worse comes to worst," which indicates something has degraded from one negative plane to the lowest possible.
Think about this one for a minute. How exactly is it possible to un-thaw something? Putting the item in the freezer would work, but probably won't produce the results you intended, which is to "thaw" it.
(Someone) and I
You probably know to use the other person's name first when it comes at the beginning of a sentence, such as "Brandon and I put the presentation together." But many people don't understand that when you're talking about yourself and someone else toward the end of the sentence you should use "me" instead. For example, it would be "The CEO awarded bonuses to Brandon and me." An easy way to remember this: If you remove the other person's name it would sound weird to use "I," right?
Spell check should catch this one, but it won't help you with verbal communication. Just know "irregardless" is not a word. It's simply "regardless," as in "Regardless of what you think about grammar, you'll look silly if you use it incorrectly."
This also goes to the point that if a phrase is common enough, it merely becomes part of the language. So although unthaw is technically not correct, it's general usage has likely made it part of the lexicon. I use the trick to remember "(someone) and I" all of the time. If the sentence sounds weird when you leave out the other person's name and just use I, then I should not be used. As for irregardless, I was in law school before I understood that irregardless is not a word. I used it in a sentence with my mentor, and he instantly corrected me. That's what mentors are for, right?