Fun in PvP :
Doing good -
It does not matter if you win or lose, many times the player/team you fight is just better, but as long as you did what you could and put up an actual fight, then it's fine.
Fatality -
Doing a fatality right in the middle of the opposite team.
Duel situation -
In those rare cases where you end up on 1vs1 situation in a minigame.
Sieges -
Crushing a whole raid force trying to rush trough a breach and seeing them burn under the casters fire.
Sneaking behind a wall of casters in SW and KB them all off a wall and watch the carnage of the sins/barbs jumping on them like sharks on free food.
Minis -
Knock backing someone into the lava.
Sneaking behind the enemy, ninja their flag, and sprint back while being chased, crossing fingers for your team to show up and cover your back.
Raping a necro spellweaving on his respad.
Making an KD whore leave the game because he's afraid to get 1 death.
Releasing a massive crit on the entire enemy team, like hox pilars, conq ww, etc.
The list could go on. AoC combat system allows so many thrilling opportunities.