Dear Sefienolte,
Thanks for the question! The answer really is…it depends. If you are applying for one of the most elite schools, like Harvard, Stanford or Wharton, you might want to explain why the lower grade occurred. What was the C+ grade in? Did it occur in a year in which most of the other grades were toward the lower or higher end of your spectrum of academic performance? It’s important to think critically, and not just apply a blanket answer to your situation.
If you are applying to a lower-tier MBA program, or if your work experience, community service contributions, and GMAT scores are truly stellar, you might want to leave it alone. However, given that your academic performance is not in the upper-most ranges, you may want to provide more insight.
As you probably know, MBA AdCom’s do not look at one element (or even one grade) in isolation. However, it’s difficult to guide you without having a more comprehensive understanding of your profile. If you're just feeling lax and not really that committed to going to B-school, sure, don't explain it. But if you'd actually like to be admitted to a top MBA program, with a degree/brand worth including on your CV, you may want to think a bit more critically about it...
I wish you all the best in your applications!
Regards,
VG