I had unintentionally performed a sexual act with a sex worker and only found out after.

I had a period in my life where I had participated in quite a bit of high risk sexual experiences. One time I volunteered to be pegged as part of a threesome. I met up with the participants in a gas station parking lot and followed them to a near by apartment. Once there, I was pegged by the woman while the much older man watched. He continually snorted some unknown substance and got really into it. Afterwards, the woman and I performed oral on him. As I left, the woman asked me for a ride home, which I obliged. While driving her home, I found out that she was a sex worker whom he hired just for that act, and she had assumed that I was also a sex worker. I dropped her off and never saw her or him ever again.