I actually had a rather embarrassing experience while being catheterized in the hospital. I was going in for surgery years ago and the doctor ordered a catheter before surgery. The nurse that was working me up before surgery told me that she would be shaving me and inserting a catheter. I was really embarrassed because she was young and was very attractive and I didn't want anything really humiliating, like getting an erection, to happen while she was doing those things.
She took her time shaving me and I was really nervous while she was doing it, but I managed to maintain my composure. When she was ready to do the catheter she asked if it would be okay if a student nurse watched and helped. I was hesitant, but wanted to be cooperative so I agreed.
It was the preparation that was the most disturbing.The student was even younger than her and I was laying there fully exposed to the two of them as they prepared the catheter. Then the nurse took hold of my penis and pulled back my foreskin and began to clean of the glans with some solution. She used a cotton ball soaked in the solution and cleaned me with a circular motion four or five times. All the while I was getting very aroused, but I guess because of the embarrassment I didn't get an erection.
Then with the student watching very closely she squirted some lubricant into my urethra. It was the weirdest sensation almost like I was ejaculating backwards. At this point I was really frightened that some thing worse than an erection was about to happen.
Then while still keeping a grip on my penis and with the student watching just inches away, she began to insert the catheter. At that point I was on the brink of disaster. As she slowly pushed it into me I ejaculated. I wasn't looking, but I guess it was already in a little ways but not all the way because I could feel my ejaculation squeezing out of my penis and the student suddenly said, "What's that?"
I was doing my best to act like nothing was happening, which wasn't easy, but I'm sure the nurse could tell even though I never really got a full erection, I could feel my penis throbbing.
She proved to be a true professional. After a moments hesitation she said, " Oh, that's just some of the lubricant squeezing out as I push the catheter in."
She finished quickly and as she left she gave me a sympathetic smile. I always wondered if she told the student what really happened later on, but I was thankful for what she had done.