“bad” vs. “poor”

A friend of mine recently passed judgment on (what turned out to be a correct) usage of a comma in a Facebook post by saying, “That’s a really bad use of a comma.” I found myself cringing at his use of the word “bad”. ‘You mean a poor use of a comma,’ I thought to myself but did not say. Then I stopped to wonder why I had had such a gut response. Review of the Gregg Reference Manual, AP Stylebook and  the Chicago Manual of Style, as well as a quick Google search for Anglicistic discussions about the usage of “bad” vs. “poor”, and consultation of Webster’s New World Dictionary for the definitions and usage of both words, brought me to accept a consensus that there is no difference between the use of “bad” and “poor”, as they both essentially mean the same thing (“not good”). Just the same, I will continue to go with my gut as to which sounds better in what context.