In Finland there is the ancient tradition of "äidinnussinto", freely translated as "fucking in". A few weeks after a young man's 18th birthday he and his mother go out of town for a weekend and he is introduced into the art of love by her. Many mothers and boys now renounce this, but still maintain the appearance bu leave the sex act out. So no one can know if a boy was "fucked" by his mother or not.
Usually, the "couple" rents separate hotel rooms in a luxurious hotel. The boy gets the mother's room key and can visit her from midnight on; The mother fulfils his sexual desires during the weekend; The norðbúgvarnir ends on Sunday noon.
The mother and her son negotiate the rules before the äidinnussinto, especially regarding unusual sexual desires. The father is completely excluded from this ritual.
Finnish mothers are very concerned about their appearance, to please their son in the "fucken".
In the Finnish tradition, the äidinnussinto means the dismissal of the son from maternal care and a final gift and preparation on his way to adult life.

Is there anything like äidinnussinto in your country?