Very interesting question, but difficult to answer.
As a child, my mother took often ( fairly frequently in fact) my rectal temperature. She was allways very nice and gentle. She used to tell me stories, as the thermometer registered, and I enjoyed those moments of innocent intimacy, but I was allways afraid that I would in fact have a temperature and my mother would call the doctor, my biggest fear at this age.
Then, just as I turned 18, I had my last high School physical. During this exam, to my surprise, after the genital exam, the young and attractive female school doctor asked me to turn around and then, without notice, parted my buttchecks and incerted a thermometer in my rectum, letting her hands on my buttchecks as the thermometer registered. She must have done a good job as I quickly developed a full size érection. That was a humuliating (two others ladys were present) but also exciting experience. I still remember it, fifty years later
A few years later, I fell in love with a fascinating girl, who happened to be very much into medfet. The first night we had sex, she produced a stethoscope and a thermometer and had me take off my clothes. Then she stethed me and took my rectal temperature before accepting to take off her own clothes. She certainly did a good job that night. And so she did for the four years that our relation lasted, as she insisted to take my rectal temperature every time we had sex. Of course, she also allowed me to take her temp
Now, for some times, I have been enjoying a happy relation with a girlfriend, who likes as much rectal temperature as I do, and we play a lot with thermeters every time we make love. She also does a very good job taking my temperature and letting me take hers, usualy on eachover's lap. We both enjoy rectal température, but we also have a lot of ''regular'' sex.