I had been chatting with a woman online years ago. She revealed that she had a fantasy to watch a man use a dildo on himself or to peg him - she said just the thought turned her on immensely, but no-one would cum to her party with that idea.
One night she asked if I'd like to come round and help her fulfil her fantasy.
Jumped into the car, after some prep and arrived at her house post-haste. She led me to her bedroom, and on the bed were two "devices" - a smaller, rigid strap-on and a huge double ended, fluorescent pink, soft and flexible jelly type dildo.
She was very keen to start, but I wasn't allowed to touch her, or she said she would cum there and then and it would be over before it started.
Never one to disappoint, I said that maybe we should try the smaller strap on first. She rapidly strapped in and tried, but I had to ask her to stop, as it didn't feel comfortable. She was very disappointed (as was I) as neither of us thought "Mr Jelly" was an option. It was HUGE!!
"What about you slowly try the jelly double ender on yourself first?"
GULP - OK, I'll give it a shot.

So, she set herself up at the headboard with 3 pillows so she could watch whilst I put my legs over her legs with pillows supporting my back and sitting at the other end of the bed so I could play, watch her reaction and she could see what I was doing and watch my reactions.
I covered my perineum and inside me with LOTS of lube (provided) and slowly - oh so slowly - pushed Mr Jelly in. Despite my fears, this one felt rather good - not uncomfortable at all.
As I was doing this, her mouth hung open and she nearly came watching and urged me on. I think I got about 30cm in and I suggested that maybe she would like to take her panties off and slide the other end of Mr Jelly into what appeared to be a now dripping wet pussy.
Her now soaked panties hit the wall immediately and with a well practised movement, she slid "him" into her, now, very tingly and slippery pussy.
Then two things happened.

1. She moved closer to me and grabbed hold of my cock and started to masturbate me. I've never felt anything like her touch - it was not too soft and not carelessly hard. I couldn't have done better myself and I've never experienced anything like it with any lover before or since - she really knew what to do with a cock. Possibly, the rubbing in the prostate area by Mr Jelly helped - I don't know - but it was mind-blowing.
2. Secondly she started to move back and forward with her pelvis, forcing "Mr Jelly" back and forwards between us whilst continuing to masturbate me. I started to mirror her actions too.
Jesus wept - if I had died then and there, it would have been my ultimate experience. We continued sawing back and forward until I thought my cock was going to burst - it was now an angry pink and about an inch longer than it had ever been. She was in a similar, but more feminine state and asked me to rub her clit now.

My eyes (and hers) rolled back in my head as she and I came like never before.
She thanked me repeatedly for fulfilling a fantasy of hers.
I had a new fantasy now - to repeat what had just happened...