I've played footsie with girlfriends over the years, but the first thing that came to mind when I saw the thread title was this:
At a meeting at my last job I sat down next to a co-worker who was interested in me. After a few minutes I felt a slight pressure on my left foot, but forgot about it and focused my attention on the meeting. After the meeting was over I felt the pressure come off my foot. Wondering what was going on I looked down to see my co-worker slip her bare foot back in her shoe. So, she was basically playing footsie with me for the better part of an hour, in view of the entire department, with me none the wiser. Completely unprofessional of course, and a little embarrassing, but no one said anything, so no harm done. And yes, she did have pretty feet, which she (and I) felt were her best feature. Unfortunately, her other features were lost on me. 😉