My son's "best tip" story was about a couple that sat in his section and he had just finished slicing bread and didn't realize he had cornstarch and crumbs on his black pants. He always says he can tell just from looking at his patrons what they're going to be like, and he wasn't getting a good feeling. So he went up and introduced himself as he usually does and right away they lambasted him, saying: "You're disgusting!"
He was dumbfounded for an instant and then tried to recoup and asked if there was anything he could get for him and she continued to attack him, mostly over his clothes being "crumby." His colleagues heard what was going on and offered to take the table.
"No," he said. "I've got this." His professionalism led him to take it on as a challenge to keep his feelings out of it and win them over.
I'm not sure what he did to serve them from that point on, but when they left, he picked up the receipt and on a $70 charge they had left him $140.00 tip.