You know what would be fun and/or interesting, a playthrough where you manage to max out rivalry with EVERYONE. I'm assuming you'd have to start with a mage Hawke (so you get Carver, who is already deep in Rivalry Hell) and then do the opposite thing you would to friendship everyone. Take Fenris to quests where you support the mages and take Anders to quests where you support the Templars. Refuse to give Merrill the thingy in her companion quest, which nets her a big ol' boatload of rivalry (unless you're +100 friendship with her which I always am at that point xD)