I wouldn't exactly say I'm a grammar freak. I make my own share of mistakes. I just happen to have "Grammar Girl" and the "Chicago Manual of Style Online" bookmarked. Several grammar books have permanent residence next to my computer. I correct my family and friends on Facebook because I get a kick out of making fun of them. And since I'm a writer, they think I have the clout to do that . . . (I won't digress into another post about misconceptions people have about writers.)
The great thing about writing fiction is that you can flaunt grammar rules in the name of poetic license most of the time. Like above. Did you notice the sentence fragments? (I didn't pull one over on you? You don't think "Facebook posts" is a complete sentence?) There is one thing that, if your MS crosses my desk--or my screen, I should say--I will mark with fervor.
If I've edited for you, chances are you've seen the dreaded comment with two little, annoying letters "cs" over and over. Don't worry about it. I'm about to lecture now, but quite honestly, it's by far the most common mistake I see in manuscripts. There are several in the first Harry Potter book, just sayin'. Sometimes--but only when I can clearly see the reason the author punctuated the sentence incorrectly--I let it slide.
Simply put, a comma splice is when a comma is used to split (or splice) two independent phrases without a coordinating conjunction.
Example: I went to the store, I bought bread.
Wrong. WRONG! . . . (Sorry, I'm calm now.) Although the two ideas are closely related, and it's quite tempting to emphasize the relationship by using the comma as just sort of a breath between them--it's wrong.
If you want that close relationship use a semi-colon. I went to the store; I bought bread. Or better, reword the sentence. I went to the store and bought bread. OR When I went to the store, I bought bread. The possibilities are endless.
I personally think "Grammar Girl" has one of the best explanations for what comma splices are and why it's better not to use them, despite the temptation to flaunt this particular rule in the name of art. Read or listen to it here.
In the mean time, stop splicing those sentences incorrectly.