Has happened to me only once and it was done so skillfully I didn’t know it had been done.
It was during the best massage of my life in Hong Kong. I was having some suits made and the man took me through a labyrinth and we entered through the back door. He introduced me to a young lady and said he would be back when I was done.
I’ll leave the details of the masssge for another thread. At some point the hand job became a blow job but it wasn’t until she got up to ride me did I notice that I was wearing a condom. I’m not a fan of rubbers but in this kind of setting it was probably for the better and to this day it’s the best massage and happy ending of my life.