Cow Tipping

Cow tipping is a sport found in Fallout 3 and Fallout: New Vegas

To play, all you have to do is sneak next to a [Brahmin] with your weapon holstered, and press the action button.

However, various random encounters take this sport to a whole new level.

Fallout 3:

Near Oasis, high in the mountain on the edge of a cliff, a Brahmin may spawn. Push it off the cliff, and watch it fall. This type of event may also occur on raised highways near the edge. Some near lakes too.

Also, the Lone Wanderer is not the only one who plays this sport. Another random event when under a highway or cliff may occur, where a Brahmin suddenly crashes to the ground near the Player.

Fallout: New Vegas:

While cow tipping is no longer a random event, if you have the Wild Wasteland trait, going near the cliff close to the fort may trigger a Brahmin to suddenly crash to the ground next to you.