I don't think they are labeled "Unisex". They are usually posted as "Companion Care", or "Special Needs". They have them at the RCC in SFO. Sometimes they are referred to as family restrooms. They are alos for fathers traveling with young daughters who don't want to use the mens room but don't want to send their daughter in a restroom alone. They are becoming more common in airports and shopping malls, and work well IF people don't abuse them. Basically if you don't have special needs don't use them. The FA likely just wanted a private bathroom. Not cool to leave people waiting like that.