The researchers found people who were feeling good about themselves used more direct language and were less polite when asking for things than others. The more difficult the situation, the ruder happy people were.
Experts believe that this is because when someone is in a happy mood, they feel more confident, overestimate their chances of success and - because they prefer direct solutions - underestimate the likelihood of giving offence.
In contrast, the researchers found that those who were in a bad mood used more indirect and elaborate language to get what they wanted.
"People in a bad mood were more cautious and polite than those who were in a good mood," said Joseph Forgas, of the school of psychology at the University of New South Wales, Australia. "It seems that they have a more pessimistic view of the success of their request and so give them in elaborate and indirect ways."
The research, published inThe Journal of Personality and Social Psychology, involved 368 students in three different experiments.
In the first, 120 participants were asked to write down an event that had made them very happy or very sad, to induce that mood. They were then asked to how they would respond in different scenarios.
For instance, they were asked what they would say if they were at a dinner party where the host was a proud cook but they wanted some ketchup. Responses ranged from "This meal might need something?" to "I want ketchup".
The researchers found there was no difference between men's and women's level of politeness. Those who were in a good mood were twice as likely to be rude in their requests than those in a bad mood.Reuse content