I've probably had a few more but recall only two. Used to fly Biz as a kid (lucky) back when Biz seats were not as nice as now.

Was flying back from Japan to the US (LA? SF?), most likely on Northwest back when it was JAL, Pan Am or Northwest only, and I got bumped from Biz to First. I don't think I had status as I don't think they had such things back then. Was my only experience in first trans-pacific. Was nice, but probably would be much nicer now.

I had a bump from economy to biz once going to Japan on ANA JFK-NRT. No idea why. I had a lot of miles on United, not even in the ANA program. But they called my name at the gate and I was upgraded. Again nice, but no lie flat seats back then. Still couldn't sleep a lick.