My long term swing buddy got into it when I was trying to get her to try anal. She asked, "If it feels so good, how about I use my new strap-on on you?" What could I say but, "Of course, Honey!"
I did and she did. She was very good at it, lubed and loosened me up with her fingers, and eased the head of her 9 inch strap-on gently in and out of the entrance to my ass, going deeper and deeper each time. Soon it popped past my sphincter and I said, "Oh!" She asked if I was OK, and I told her what had happened and that it now felt OK.
Gradually she went deeper and deeper, until she was balls deep. She proceeded to fuck me for about 20 minutes, with the veins the strap-on making the nerves in my ass vibrate with each stroke. Then my hard cock came, and came, and came; so she stopped.
We posted a photo of her getting ready to peg me on our swing site profile, and soon dozens of guys who said they were straight were begging to join us so she could peg them. We got together with a lot of them. Generally she would have them lay on their back and stoke their cock while she pegged them. She loved to make them cum, and when they did they would shoot fountains of cum on the air. They all said it was the best orgasms ever.