If someone has not already done so, allow me to posit Scalzi's Law of Online Communication: Anything bad you ever write about someone online will get back to them sooner or later. People who don't believe this law are by all means invited to prove me wrong. Note that this invitation comes with the explicit warning that if you write me something that says “I called my mom/dad/co-worker/whatever a hideous gasbag on my Web site five years ago and s/he doesn't know,” I'll merely forward the note to them with my compliments—Scalzi's Law works because a) people can't not tell other people about their online exploits and b) other people can't not tell about your online exploits, either. If you don't want people to know what you really think about them, don't put it online. Ever. Really, it's just that simple.
I don't have much to add to that, other than it can happen in the print world as well. Surprisingly so.
I learned this the hard way.
It was 1987. I had just started a humor column for the college newspaper and I had just written a screed against my high school English teachers (no, it's not online and for good reason. Heck, the editor should have axed that column but it still ran. It wasn't until a semester or two later did I get an editor who actually edited and told me a few of my columns were not fit to print and for that I'm thankful).
Of all my columns I wrote (and I wrote the column for three years) that was the only one to get back to my high school. And boy did I hear about it. I felt bad then; I still felt bad ten years later at my high school reunion (and felt relieved that none of the teachers I wrote about showed up) and I still feel bad about it now, but the paper itself is long gone and I doubt if you can even dig up back copies at the library so that particular piece of journalism is long dead and buried.