It is dangerous to be America's enemy, but fatal to be America's friend.

is a dangerous enemy.

Nothing is as dangerous as an ignorant friend; a wise enemy is to be preferred.

An unsuspected enemy is doubly dangerous.

And this was your friend?" Cordelia raised her eyebrows. "Seems to me the only difference between your friends and your enemies is how long the stand around chatting before they shoot you.

Enemies disguise as friends and friends as enemies.