That was precisely what one of my early trainers did to me in the schooling ring at none other than the Hampton Classic (for those who don't know, one of the snobbiest hunter/jumper shows in the country, imo!) I was probably still in my teens at the time and needless to say I was mortified (these days I might actually be able to see the humor in it ;-) but we did manage to get a few good schooling jumps in right away (just to speed up getting the shirt back on the half-naked trainer) and through the in-gate in record time! And as I recall, we had a pretty good round!
I’m just glad it was a single fence and not an in-and-out, as he was running out of articles of clothing and I’d hate to see what came off next... That would have made for an entirely different kind of article in the newspaper :-\
If you're anything like me, you've had lots of embarrassing horse show memories. I’d love to hear your stories!