One of the features I really want in both Facebook and Twitter is the ability to mark people as enemies. Starting with a small number (eg 100x) of friend/enemy

One of the features I really want in both Facebook and Twitter is the ability to mark people as enemies. Starting with a small number (eg 100x) of friend/enemy labels, they can use graph analysis algorithms to infer my level of friendship or antagonism towards everyone in the network, following the ancient principle that the enemy of my enemy is my friend. It would be very helpful for me to be able to click on a new person's profile and see how aligned we are. After all, I don't want to go to parties with my enemies, I don't want to work for companies run by my enemies, I don't want to contribute to projects initiated by my enemies, etc, and I assume my enemies feel the same way about me.