One of my favorite tricks it to put the wrong post in the wrong position.
I am ashamed to tell you how many times I have done this BONEHEADED move, so I will not.
- wait until the beer is carbonated, chill it and vent all the pressure through the "pressure release valve or the "In" post.
- Quickly loose both and place the correct post in place.
- Charge the keg, VENT, and charge again
You should not loose any beer.