I've just remembered a scary experience I had on a yacht with a weird fellow learner
we were learning to sail for 5 days and had on board 2 women who were friends two blokes and me in addition to the skipper and one of the blokes was evidently a total nutter/troll
can't go in to all the details but every time someone said something he echoed it eg I've got a dog called charlie then he had one, my cousin was killed in a car accidnet so was mine, my brother is a surgeon at St thomas's oh he must know my brother then etc to begin with we others just tried to laugh it off but he got odder and odder and being confined on a boat with him was really spooky and unpleasant..we eventually concluded that he had just been released from somewhere...
the week culminated with all of us managing to escape ashore without him and when we came back he was in the water in the harbour (although he said he couldn't swim) practically underneath a ferry...
he also had a way of taking every opportunity to grope...