I posted a version of this a few years ago here, but this really happened to me by my ex-wife several years ago and since she gave me no warning and just did as she pleased with our pre-existing D/s consent rules in place, it was definitely a consensual-but-unexpected enema rape.
I can't imagine having enema sex without a double balloon catheter inflated in one or both of us. My orgasmic contractions, even at my age, are so strong they can even push out a large plug. The most memorable one I ever had with a partner was about 2005 when with no warning, my ex dressed me completely in black latex and very high Converse sneakers and handcuffed my wrists and ankles together. After a good deal of playing with my anus with various things and her fingers while frequently telling me that she had intense plans for my submission that evening, she put in and inflated a double balloon catheter. Then she ran in a fast quart or 2 of saline and started playing with my package and massaging my belly, but wouldn't let me orgasm. Without warning, she puts my legs down together and rolls me up into the comforter I'm lying on so I can barely move and then says something about coming back later! Complaining that she can't leave me like that gets me nowhere. I hear her moving around and then water running, and she comes back every few minutes to reach her hand in and stimulate me. finally, she comes back, asks when I want my second enema and then runs in another 1.5 quarts while I can't move. After that, she tells me she'll release me from the comforter but I have to make her come at least once before she'll let me come. I get unrolled, squirm over to her on the bed, and probably spend a half hour giving her intercourse and oral sex before she has an orgasm. Having sex in the rubber and listening to the water slosh around inside me was very intense. Finally, she makes me cuddle with her until she finishes her post-orgasmic nap and then lets me work on my own orgasm with her helping, including her hands, mouth and riding me. The only reason I didn't spill everything during the ensuing orgasm was she had been kind enough to leave the catheter inflated in me the whole time. I'll never forget that night. We did similar things many times over the next several years until breaking up about 5 years later. She later confided that one of her secret sexual fantasies was to get an enema from me, and I was really looking forward to it but we broke up too soon to accomplish that.
So, yes, I've definitely been enema raped by my ex, and loved it.
Eric