I love reading studies about odd things. For instance, if you are a waitperson you probably are concerned about the tips that you receive from customers. One way to increase tips might be to leave a joke on a card with the bill.
Someone conducted a study about tipping at a bar. Each person in the study was randomly assigned to one of three conditions, no card with the bill, an advertising card with the bill, and a card with a joke on it with the bill.
They found that a higher percentage of customers gave a tip in the joke card condition than in the other two conditions. In contrast, the difference between the advertisement card and the no card, the percentage of people tipping was not statistically significant.
These findings indicate that humor may increase tips. One possible explanation of the effect of humor on tipping is that it reflects the reciprocity principle, which suggests that we should help someone who helps us. Providing a joke on a card can be viewed as helping the customer and it may make the person more happy and cheerful. The customer, in turn may wish to reciprocate by providing a tip. That reminds me of a joke about the waiter and a spoon. . .