In original native culture of Thailand, when males reach the age 18 they participate in a ceremony as follows:

They stand naked in a large circle, facing inward. A beautiful naked girl does a sexy dance in the center of the circle. Behind each male is a beautiful naked girl. As soon as all the males are excited and have erections, the girls behind them reach through between their legs, pull their erect penises downward and backward..............then release them. Their penises spring back up and go "WHAP!" against their bellies. This is an ancient Siamese measurement of strength of masculinity. And that's why the capital of Thailand is called Bangkok.