This happened a few years back - I think I was about 16 at the time.
A group of us had been to see a show at a local the theatre by a fairly well known hypnotist. It was pretty typical of the genre: some volunteers go on stage, are hypnotized and do stupid stunts.
Afterwards we all ended up back in the room of one of my friends and got into a discussion about the show. One of the guys was convinced it was all a put up job while one of the girls was sure it was real. The girl (Jane) said she could settle the argument by hypnotizing one of us there and then. We laughed but she was serious and asked who also believed in it. There were only 2 of us: me and a girl called Angie.
Without giving us a chance to really say no, Jane said she would hypnotize us to prove it worked. She basically did the same thing as the stage hypnotist: she told us follow her instructions and to watch her finger as it moved. It was strange but I soon found myself relaxing and follow what she said very easily. I did not feel sleepy but I remember being relaxed and happy to go along with what she said.
Quite quickly she declared we were both hypnotized. I did not exactly feel hypnotized but I remember just sitting there not aware of much going on around me apart from her instructions. I remember she told me my hands were glued together and then not being able to pull them apart and after that she told me she would put me deeper and I would would not remember much until I came round. After that, all I recall was her starting to talk to me and then hearing her count down from 5 to 1 and my coming around.
I felt pretty normal and wondered if that was it and then saw the rest of the guys laughing. I looked across at the other subject, Angie, and was surprised to see she was totally naked - her clothes in a heap by the side of her chair. She didn't seem to notice, but looked at me and laughed.
Jane said thanks for helping and did I feel ok? I said yes.
'Are you sure?' she said.
'Of course I replied, why shouldn't I?'.
'Doesn't it feel strange being naked?' she laughed as she said it.
'But I'm not!' I replied. I was convinced I was fully clothed.
At that she whispered something in my ear and I suddenly realised she was right. I guess while deeply under she had made me undress and then forget I had.
She then spoke to the others and asked if they were convinced. They all agreed. And I bent to pick up my clothes and get dressed.
'Not so quickly.' said Jane. 'I've one final demonstration. Just sit down for a moment. It won't take long.'
At that she came over and whispered something in my ear and then did the same for Angie. When she had done it, I remember becoming very, very horny and feeling my cock harden. Almost as soon as I realised I was horny, Jane asked us:
'Are you horny?'
Both of us quickly said yes.
'Then do what you usually do when you are horny.'
At this I remember grabbing my cock and frantically pulling at it. I did not care about the audience I just wanted to cum. I was vaguely aware of Angie rubbing herself as well. I got very, very turned on but could not cum.
'Do you want to cum then?' asked Jane.
'Yes!' I shouted.
'Say Please Jane' she said laughing.
'Please Jane' I said and heard Angie say.
'What do you think, shall we let them cum?' she said to the others. They laughed.
'Oh alright then. Here's the magic word: Elephant.'
At that I felt myself shudder and I came hard, squirting a white mess on the floor.
At that Jane handed me some tissues and suggested I clean up in the bathroom and I ran off with my clothes in my hands.
It was a very, very weird experience and to this day is often the subject of my fantasies. I certainly am in no doubt about hypnosis - if I were all I have to do is remember the time I was made to jerk off in front of my friends and felt the whole thing was perfectly normal!