There are literally hundreds of ways to narrow people down. With some simple sleuthing and a little patience, people can find you based on even the smallest detail.
Seeing where you've been...
There was a time when Graph Search would allow you to easily find out what parties someone's been to, or locations they've checked into. And while you can no longer find those things out by submitting queries like "places X person has been in the past X months/years" or "events X person has attended," there are third-party websites like this one that will easily uncover and organize that sort of information for you.
... and what your interests are
Unless you've Fort Knoxed your privacy settings, anyone can easily find out the bands, movies, books, websites, people, or groups you like using the aforementioned stalking site.