Eat Lead: The Return of Matt Hazard

When you are behind cover put your cross hair on an enemy and only pull the right trigger to fire. Rinse and repeat 25 times and you will get the achievement. Enjoy!

Adding to WolfVelocity's description of the method, I found the best place to farm these is on the Level "Same Ship, Different Day". I would suggest farming, as the blind firing is pretty much next to useless in the main game. Using this level, you are working to a secure area, you can take your time, and control the enemies in it.

The level starts with you in a room, move forward, take cover behind the concrete pylon in front of you.
Shoot the guys that rush in (there are about 5-6).
One turns into a Zombie, so you will need to focus fire to kill him.
Leave one guy alive to kill you, when all the others are dead through blind firing with the Hazard Pistol (respawning weapon point in the corner closest to you if you need it) walk up to this guy and let him do his worst.

You start again at the opening, step forward, take cover, rinse and repeat.

Very quick and easy location to get this one, took me about 10 minutes with reloads and the inaccuracy of the blind fire.