At showdown, the player in the earliest position must show his hand. After that, it will go clock-wise (just like on a flop, turn or river) and all the other players have the option to show or muck. If they muck, they can't win the pot.
So, to answer your question: if the guy with AK has the earlier position, he can't just muck and forfeit the pot. He MUST show his hand.
PS: I rarely show my hand if I see that I'm beaten. The only situation I can think of when unvoluntarily showing your hand can be a good idea is if your opponent(s) is/are on tilt. If you have the chip-lead, it's a good idea to win a pot and show that you weren't bluffing. They'll be 100000 % sure that you're bluffing a big percentage of your hands, but those legit hands that you've shown will be so well locked in their head, that it will be very hard for them to play their small stack against you. The blinds will kill them eventually and you'll go up the payladder :) .