First time we took our daughter in law they asked her if she washed her hands in the bathroom. She said yes. They asked the color of the soap. She guessed wrong and had to go back and wash again.
I overheard something similar to that once! There was a guy (not in my group) who had come back from the bathroom, and a waiter asked him if he washed his hands. When he said yes, the waiter asked if the soap was liquid or a bar of soap. I might add that it was powder soap at that time (this was at least 10 years ago), so neither one would have been correct.

As for stories involving my own family, there are lots of those, too. For example, on my very first trip in 1997, my mom didn't finish her green beans. The guy whose name tag said "Dad" (for those who don't know, they always have two older CMs playing "Mom" and "Dad" there) came over and did the "here comes the plane" thing and made my mom eat more green beans.
Another one involves a trip with another family that my family is friends with. This group had a total of 4 adults and 5 kids, so we had a table for the adults and a table for the kids. All of us kids ordered the peanut butter and chocolate shakes, and one of the girls from the other family knocked over three of them. The waiter came over to clean it up, and we saw that his name tag said "Topher," so my older sister and the girl who had knocked the shakes over (they're the same age) started calling him "Topher the gopher." His response was "you know, when girls your age make up poems about guys, it means they like them." Similar antics went on throughout the meal, and I sincerely hope our parents tipped him well (this was before the dining plan or anything similar existed).
Most recently, my sister and I went there on our trip in 2011 that was just the two of us. Our waiter basically was Neil Patrick Harris' (Barney from How I Met Your Mother, if you didn't know) lost twin, both in appearance and behavior. He gave my sister crap for texting at the table, plus he accused her of licking her plate when he saw that she had used her pork chop to wipe up all the barbecue sauce on the plate. He also had some hilarious responses to the light-up MJ glove I had gotten at Captain EO and brought there with me (we had hoppers). The best, though, was when he found out she was celebrating her birthday and brought her an ice cream sundae with popcorn as one of the toppings.