A Comma'N Problem

Merriam-Webster's Pocket Guide to punctuation lists 44 comma rules! No wonder it's hard to know whether to use one or not. One hint to help: if you can put two phrases together using and, but, or, no, or so and be left with two complete sentences, use a comma before the conjunction. For example:

I am writing this blog post, and it is hot outside.

I am writing this blog post. It is hot outside. (Two separate sentences could be formed which is why a comma works well in sentence one before the conjunction.)

I am writing this blog post while it is hot outside. (No comma because there is no conjunction.

I am writing this blog post. It is hot outside.

I am done writing this post. I will probably, maybe often, misuse commas and I will forget the rules.

Question: What punctuation mark gives you the most trouble?

Adapted from an article originally written by Brenda B. Covert for PROfile.