Why do they say - "people need to have sex more, they will become kinder", if someone is in a bad mood, it means "not fuck"? Is there a connection?

These are evil tongues spoken. There is no connection from malfunction. But still, there is a slight correlation between satisfaction from sex and mood.

It is from muffins that they grow kinder and from mustard they are upset.

I'm probably ancient for such questions, I'm 68 years old married with my only man 48 years old, plus they were friends before the wedding for 5 years, classmates, in those days there were completely different norms and morals of relations, we are monogamous, but I will say about sex, he is very important in a relationship between two people, this feeling of significance for another, this desire to do everything for this person, this is flying all day on wings and thinking to yourself, it would be faster for the night and in bed, it’s not even thinking about treason. Maybe old-fashioned, but in my understanding, sex is only with a loved one and nothing else.

This idiotic phrase is usually addressed to women, with interlocutors of both sexes. Women thus emphasize their own demand for the opposite sex and "love", that is. assert themselves at your expense. Men, on the other hand, simply broadcast their vision of what a woman should be in order for them to like it. She must definitely love sex. But here's the paradox - you should definitely want to have sex with this man and only with him alone. The option "but I love sex so much, it always makes me in a good mood, so I will do this with all nice men" does not work.
P.S. The importance of sex is generally somewhat exaggerated. Lack of sleep causes bad mood more often.

Yes and no. In general, sex is one of the basic needs. Therefore, the lack of it on average affects mood and health in a bad way. For example, scientists (not British) have found a significant connection between the lack of sex and increased blood pressure.

On the other hand, if a person in his 40s has never had sex, or he has a negative experience that influenced everything subsequent relationship - even if he has a super-skillful permanent partner (which, in general, is almost unrealistic) - due to the formed incorrect attitudes in the sexual sphere, and the lack of the ability to get pleasure from sex - there is a large share of doubt that this will be beneficial action.

The deprivation of sex from people who are accustomed to receive it often and well - of course, leads to a deterioration in mood, and in the case of mental workers - its productivity decreases just critically :)

It happens that there is a connection, it happens that there is no connection. Only the idiot does not understand that the lack of sekas is not the only reason for a bad mood and irritability, there are others (thousands of them). So even old Freud did not reason, contrary to stereotypes.

In general, of course, there is a connection. My sister, when she found herself a bull, immediately began to return home at 3 in the morning. She suddenly made a curl, used makeup, although she did not like it before. And in general, she came very happy and favored, kissed, after which she quickly ran away without spending the night from home. Before that, she often behaved like an authoritarian bitch, and then suddenly estrogen flooded, she immediately became a charm. Then the truth all the same returned to the default state of the bitch, but ... the sinful, sensuous experience left an imprint, nevertheless it changed a lot with the martyr and without the martyr. The girl was a sad crocodile, and now she is almost "celeba". I'm happy for her.

Of course not. There was just one pervert at one time - Freud. It all started with him. He believed that any problem was related to sex. Are you tired? No money? Looking for the meaning of life? - No, no, you just don't have enough)
Naturally, this explanation suits many, but it is hardly true.