That's a good one, Linda! It looks like not too many people are willing to admit their most embarrassing moments. This isn't really one of mine, but my youngest son's.
On our first Caribbean, my oldest son (then 10 yrs.) stayed on the ship in St. Maarten while my husband, my youngest son (then almost 8 yrs.) and I went into town to do some shopping. We were in a store, buying some neat looking surfboards when my son, in his boredom, started swaying forward toward the counter.
St. Maarten stores, being what they are, didn't have a 'real' counter. The cash register was on 4 pieces of wood planks in the shape of a square with the center area missing. Instead of a back wall, there were just touristy-type items hanging down. As my son swayed forward, I thought, "I hope he knows there isn't a back to that counter." He didn't and went flying right through the counter! He was mortified, but we all died laughing because there aren't many people that fall through counters.
The poor little guy started crying from embarrassment and that put an end to our shopping for the day. He eventually was able to laugh at it too, as we knew he would. To this day, I will never forget seeing him just lean forward and go right through the counter and the look of shock on the shop girls' faces!!