Back in the 80's my friend was locked in the bathroom of TWA L-1011. It was a red-eye from SFO to JFK. She and I were sitting together and she got up to use the loo and got locked in. I noticed she wasn't back after about 10 minutes but just thought she was in the back smoking. One of the FA's finally heard her banging on the door after about 30 minutes. It was a hoot however she didn't think it was so funny.