While browsing through another users reputation, I noticed an entry that sais "-15 unaccepted". Since I have answered a question and was not accepted in the end, I checked my own rep and found nothing of the sort.
According to the FAQ the only way to lose rep is by downvotes and even then only one or two points at the same time.
Now I am courious to know under which circumstances one can lose rep by unaccepted answers.