Sometimes I just don't know what goes through people's minds

I realize that not everyone is a full time eBayer and not everyone looks at their eBay activity as a business, but there is so much I see on eBay that just makes me wonder what goes through people's heads.
I regularly read and participate in a discussion board that is meant for people who are using eBay as a business, so for the most part the posts are from people honestly trying to either help or get help. It is a pleasant place to spend downtime and a great place to get an outside perspective when I get stuck in a dilemma.
However, the other day someone had posted something there and I clicked their feedback number just to check them out.
I was shocked at the feedback they had left for someone. They wrote that the buyer was a pain in the butt even before their payment was received! I just can't comprehend writing that about one of my customers! And it upsets me even more that this person is not a newbie or someone who just sells one or two things here and there. This is a person who is a regular seller and is looking at their eBay activity as a business. How can someone consider themselves a professional and post that a customer is a pain in the butt, and post it where it is permanent and public?
Maybe it was all those years I spent in the service industry, or maybe it was the manors that my mother taught me, but, boy am I glad that I know better than to treat people that way.
It just upsets me because I would love eBay to be a positive experience for everyone. Please, fellow eBayers, remember the golden rule.