My last one would be around age 5 or so. I remember distinctly the nurse at my pediatrician's office taking it orally for the first time.
At this office, they used to take you back, get vitals, then return you to the waiting room, only to bring you and your mother back later to sit in a room and wait for the doc.
Well, I was returned to the waiting room where I told my mother triumphantly, in front of everyone else, that they had taken my temperature in my mouth, so now I was "a big boy and she did not need to take it in my bottom any more". There was much laughter, and my mother looked like she wanted to die.
It did not hurt when the nurses took it; except for having to lie there and do nothing, I did not mind it. When my mother took it, it hurt a lot. I remember laying on the living room floor, crying and fighting them trying to take my temp. I don't think she lubricated it, or at least not well. I remember her sending my father off to see if he could find some lotion, and yelling at me to relax or it would hurt more. The more she talked, the more scared I got and the more I clenched.
As an adult, I can take my oral temp four times, probe placed properly in the heat pocket, and get four different oral temps. I've tried it with different thermometers, including hospital Ivac and Diatek. I don't know what is wrong with my mouth. I have some serious medical conditions, so I get a lot of exams.
Most of the time, I wish they would take rectal temps on me. Not because it turns me on, but because I often have a low fever and it does not register on an oral temp. I realize that rectal temps are about 1F higher; I'm taking that into account here. Do enough oral temps and you will find a fever. But I'd rather have one rectal than four orals. Plus, the staff rarely listens to the patient on such things.
I do find rectal temps turn me on in a play situation, but experience has shown that play is totally different from reality. Rectal exams in play turn me on as well, and in real life they are unpleasant at best.
Plus, I consider it seriously unethical to get a medical professional to do something to you purely for your own sexual pleasure. That's totally disrespectful toward them.
If I did not think people would think I was weird, I would ask for rectal temps on me if I felt feverish. When I am okay and I know it, I don't really care if they are off by a degree...