I have only used it once. I was really sick heading back to Paris for work and not feeling the extreme turbulance. The lav was occupied forever and I told the FA what was wrong and she was kind enough to figure out why the pax was in the lav for so long for me. I just didn't have it in me to stand and pound on the door myself.

(ps: It was a totally non-contagious sickness...I don't like passing germs )