Without a doubt having my temperature taken both in the mouth and in the butt when I was 8. For whatever reason I enjoyed chewing on the oral thermometer (perhaps it relieved the discomfort of the thermometer stabbing me under the tongue). My mom didn't correct me for chewing, so I assumed she had gotten the reading she had wanted.
My mom led me to her bedroom rather than my own which should have set me off something unusual was about to happen. When she unbuttoned my pants and laid me on my stomach leaving my underwear up I became increasingly concerned. My mom had never given me a shot in the butt before and since she wasn't a nurse, I figured she couldn't.
Still every doctor visit I ever had that the nurse said he needs to be in his underwear always meant a butt injection. I saw my mom rummaging through the medicine cabinet reasonably sure she wasn't preparing a needle. Once she sat and depressed the bed next to me, I could feel her pulling down my underwear and a gust of air hit my butt. I then thought for sure I knew what was going on. She was going to either give me medicine in the butt for fever or possibly coughing. I remember the last few times she gave me oral medicine it was so gross I gagged and nearly threw up.
It was of course humiliating the idea of my mom putting medicine where I poop, but a part of me was so grateful at the idea of not gagging or barfing that I was willing to accept the indignity. Besides, last time I remember spitting medicine out, I remember how furious she got, so I was in no position to argue. My mom left the room in a flash and told me to hold still. I could feel whatever was in my butt was static and not melting or being absorbed, I looked back and saw my butt was still uncovered and had a baby thermometer placed between my butt cheeks.
At this point, I became humiliated and panicked knowing I was suffering the worst humiliation a boy could endure. Knowing my mom changed my diaper when I was a baby is definitely awkward, but knowing then my mom still felt she had to take care of my 8 year old behind left me laying there naked like a shamed infant. I was in shock and laid there on my stomach knowing just what an inferior being I was.
When my mom came back I couldn't pull up my underwear and pants fast enough. I don't think I could look at her the rest of the week in school. Once I became an adult I dated a few girls and confided in them what happened and a couple of them were sweet and understanding and one was horrified and disgusted that I wanted them to role play being a young boy being embarrassed by a nurse.