It's good to tip people for their services.
Jack is out on a date with Justine at a very, nice restaurant.
Jack wants Justine to like him a lot.
When Jack get the bill, he adds on a tip and thanks the server for such a nice dining experience.
When Jack gets the bill, he realizes he is short on cash, so he decides to forego giving the server a tip.
Justine notices the tip and his kindness and tells Jack how much she likes and respects him for treating the server so nicely adding she waited tables before.
Justine notices the $0 tip and tells Jack she likes him a lot but doesn't want to date a non-tipper as she used to wait tables.