I can honestly say I've never gotten my ass beat thankfully, in a real fight that is. I've whooped some asses, though never beat anyone down, I stop when I see they've had enough.
I have gotten a whooping in the gym though, when we were sparring in boxing class, it was my first class and my cardio was pretty shit and even though I knew the basics of boxing, I got a reality check on the differences between being trained and just knowing some things for yourself. We were alternating sparring partners every minute in class and about halfway through I was dead tired already.
Needless to say some guys didn't really take it easy on me and I got a pretty good whoopin by the end of it. One guy specifically kept hitting me with right hooks over and over, lol. I couldn't stop it. I ran into one of them and he got me on the nose flush pretty fucking hard. He felt bad and apologized but I was more frustrated than anything and told him to just keep going. I at least learned I had a pretty good chin that day. The next classes were much easier though as my body got in better condition.
Aside from that time at the gym, I got wrestlefucked 2 times during play fighting. Once was by my cousin and the other by some kid, but they actually knew how to wrestle so I don't feel too bad, lol.