I've sortof experienced that. My partner wasn't into anal when we first started dating, and the first time we tried it, he didn't like it. A few months later, we were having sex and he thought he'd just surprise me by switching to anal, since he knew I like it. What he didn't know is that without lube and preparation, I'd end up in the fetal position from the pain.
There have been a few other times where he'll accidentally slip out (during PIV), and in the heat of the moment, rush to push back in and aim a bit too low (or high, depending on the position), but he usually catches it before he really penetrates.
There have been a few other times where he'll accidentally slip out (during PIV), and in the heat of the moment, rush to push back in and aim a bit too low (or high, depending on the position), but he usually catches it before he really penetrates.