The description a bit misleading. It should read
"Get 25 headshots in multiplayer". At first, I thought someone had to shoot me in the head 25 times, but that wasn't the case.
These can be done in a private match with a friend.
Just to note, the multiplayer kill achievements are buggy. If for some reason the achievement does not unlock when it should. Go back to the dashboard, restart the game and try again. I had close to 200 kills and over 100 headshots with no achievement. After I restarted, both unlocked on the first kill. Hosting the match, helps as well.