I have to say it was the Tux and Tennir Dinner we did for a fundraiser the Houston Rockets do annualy. The dinner itself wasn't that bad, only 400 guest each getting a plated salad, plated entree, and plated dessert, plus an hors D'oeuvres reception before the dinner. It was challenging because the quality of the fish our supplier delivere was well below our standards twice so we had to send it back each time and wait for them to send us good quality fish on the morning of the event which put us behind big time. At the end tough, we were able to pull it all together for a great dinner service. How about your most challenging event?