Unlike many of y'all I guess I'm just young enough to have missed the era where home enemas were a “cure-all” “for whatever ails you”. So I never got enemas at home.
When I was a teen, I had to have minor surgery performed under a general anaesthetic, to correct a non-serious but annoying medical condition. So an enema was part of the prep for surgery, in the hospital, the night before.
I was kinda-sorta aware, even at that age, and in those pre-internet days, that this was a fetish for some people. One, I had been, since about 9th grade, a fan of Frank Zappa, and was familiar with the song “The Illinois Enema Bandit” from Zappa In New York. Two, I'd seen a “letter to the editor” in a porn mag from someone who'd discovered that he got sexual gratification from having enemas administered to him. So I knew that this was a thing, even if it seemed sort of weird to me at that early stage in my sexuality.
I was kinda nervous, because everything I'd heard suggested that this wasn't going to be a pleasant experience. I was even more nervous at the alternative prospect that I might find it a little too pleasant, IYKWIM.
You can probably guess the rest of this story. A nurse came in with a bag and a hose suspended from a pole. I'm not sure what the enema solution consisted of. Might've just been plain warm water because I don't remember much if any cramping. I was surprised at how pleasant it felt when the nozzle went in. And then the warm water started filling me up, and feeling that warmth flowing into me and the fullness was just heavenly. And, of course, I got a raging stiffie, as I did at that age for any reason or no reason at all. Eventually, the nozzle was removed, and she told me I could go to the bathroom and expel, which I did.
As strange as it may seem, knowing that there were guys who got hard from an enema helped me feel less embarrassed about having that reaction in front of the nurse. It was reassuring to think that I was probably not the only patient she'd seen have that reaction. Of course she was a consummate medical professional and pretended not to notice.
So it was the classic, “This is so weird. Who would be into this? Oh shit, I guess I'm into it."
I didn't have another enema until I got my first solo apartment in my mid 20s, which meant I could have a bathroom to myself and self-administer. (If you live with other people, it's kinda rude to block up the only bathroom.) I've been giving myself warm-water and saline enemas ever since, just because they feel nice.