I wont accept any friend request from someone I JUST entered a game with.
I find the easiest way to cull friends is to Centre mouse click on their name in the friends list... tis opens their profile in a new tab. Keep going down your friends lists continuing to open tabs.
Then go to the tabs one by one and unfriend them and close the tab.
It would be nice to have a 'View All' function for friends, with check boxes next to their names and different functions.
Sending multiple messages
delete
etc