One of my fondest experiences with suppositories is when I was around 10.
At the time we had a babysitter, because our parents were busy with their jobs. One day I had a strong headache, therefore I informed my babysitter of this, in the hope that she would give me some painkillers. As soon as I told her, I whished I hadn't done so. She told me to lay and wait on the sofa, while she went to the bathroom, with the intention to fetch something from the medical box.
When she came back, she was holding a white package with two red stripes. It was at that moment that I understood that I was about to receive a suppository. The packaging was a familiar one among italians: it read "Tachipirina", and underneath that: "supposte".
So, my babysitter told me to relax, and as she did so, she lowered my pants, and after these, my underwear.
Firstly, she lubricated my butthole with a baby cream, and after that, she kept massaging my anus until it felt relaxed enough.
At that point as she was unwrapping the suppository, she told me to calm down and that it was for my own good, even if it was going to burn a little bit.
I was afraid of suppositories then, so her advices were not entirely followed through. I kept crying and moving my legs up and down. At that point, she spanked my butt a couple of times, and repeated what she had told me before. When I was finally relaxed, she inserted the tip of the paracetamol suppository with her right hand, while keeping apart my cheeks with her left hand. After that, she pressed the whole bullet in, and inserted the whole finger until the knuckle.
Needless to say, it was very painful, and I felt the suppository burning for a little while longer, but my headache passed.
Only later, I discovered the erotic side of the whole process.