In the original native culture of Thailand, when males reached the age of 18 they had to participate in the following ceremony: 
They stood naked in a large circle, facing inward.  A naked girl stood behind each of the men.  A beautiful, naked girl did a sexy dance in the center of the circle.
As soon as all the men became aroused and developed erections, the girls behind them reached through between their legs, pulled their erect penises downward as much as they could, and then released them.
The men's penises would then spring back up and go "WHAP!" against their bellies.
This exercise was a measurement of the strength of their masculinity . . .

  . . and that's why the current capital of Thailand came to be named Bangkok.