I've started a lot of threads (almost 2500!), so now and then I'll see a thread I started derail a bit.
Or I'll post something too personal, and feel a bit of a sting from some of the comments.
At times like that, I'll regret having started the thread. One time I closed a thread that I had created, and a few people got upset with me. So I took a long sip of my artificially sweetened coffee, and stepped away from the computer.
Now I don't close threads except in very very rare circumstances (or at the request of the OP). What I'll do instead is just walk away from the site for a few days.
Do you ever regret starting a thread?