Sticking one’s naked Butt into a defenseless person's face. Ideally the nose of the recipient will rest submerged in the rectum of the one who is performing the "Berger". For full success to be declared there must be visible feces on, or around, the nose of the recipient.
Tim was pinned down, violently attempting to escape, as Michael pulled down his pants and preceded to berger him.
The act of forcing your bare skinned rear end into another's face in which the nose of the recipient is prodded deep into the rectum of the donor. When delivering a berger it is almost always necessary to have accomplices pin down the beneficiary beforehand to ensure cooperation.
Mike had been eagerly waiting with his pants down when the rest of us pinned down Tim. After a long struggle, Tim succumbed to the inevitability of the berger.