There's never a good reason to sound like an idiot.
For one, Ad People tend to throw out random words like they're free candy. I can't tell you how many times I've been in a meeting and someone said something was (word I don't know) and I nodded, trying to decipher from his/her tone whether I did good or bad.
For two, using words correctly makes you look good.
Thirdly, you need to know 301 different ways to say Get, Beautiful, Happy and Enjoy. Trust me on this.
And lastly, if you eff up the wrong sentence with the wrong person at the wrong time, you lose all credibility. You will forever be that idiot that doesn't know the difference between there/their/they're or who said pacific when you meant specific.
Promise me you won't be that guy.
Read some books. (Like the *ahem* dictionary)
Expand your vocabulary.
Keep spell check and Webster's close by.
And check out this Easily Confused Words test from Dictionary.com that spell check often doesn't get.
Here are a few more things you need to study:
Commonly Confused Words
Commonly Misspelled Words