The best place to get this is in Holland Valley
, just east of Fall's End
. There is a permanent bull spawn location here. Once here, open your weapon wheel, switch to utilities, then craft and consume "The Furious" potion. Then take out your bare fists and you should be able to kill the bull with 1 punch.NOTE:
Buying the Brass Knuckles
perk will not allow you to punch the bull to death and there is no way to unequip this item. You must instead kick the bull by clicking RS.