I am 70 and I have been having a strong rectal temperature fetish thoughout my life. This thread brings a lot of memories to me.
As a child, my mother tended to be overprotective and she used to take my temperature every time she had the feeling I looked tired or sick, thqt was about every second week. Then, I was on my bed on my stomach. She inserted the thermometer and kept her hands on my buttchecks as it registers. As far as I remember, she never took it on her lap. This lasted til I was 13.
Then, from 13 to 21, I was very shy with girls. I remained a virgin and I took a lot my temperature, often associating it with masturbation.
Eventually, I found a girlfriend at 21. She was very nice and gentle, but she was strongly opposed to rectal temperature. She never took mine and refused that I take hers.
My second girlfriend, from 24 to 28 was just the opposite. She was very much into medfet, and a bit bossy. She had set the rule that every tim time we were to have sex, she would five a comprehensive medical exam, me stark naked, her keeping her clothes on, , allways ending with her taking my rectal temperature on her lap. I must say I enjoyed it a lot.
For me, being on your partner's is the best rectal temperature taking position. I liké to feel my erect penis pushing on her hopefully naked titgh as she plays with thermometer, letting it go slowly back and forth inside my rectum.
More recently, I had a ten years relation with a fascinating ladyfriend who was as much into rectal temperature as me. We had agreed to take our mutual température, everyday, first thing in the morning, and we had a fun with it. Unfortunately, she dumped me almost two years ago and I am on my own to take my temperature. LOL.