dip your pen in gall
dip (one's) pen in gall
To write something that conveys one's animosity, anger, or malice. The critic must have dipped his pen in gall before writing that very negative review.
dip your pen in gallwrite unpleasantly or spitefully.
Gall is another word for bile, the bitter secretion of the liver; it is used in many places in the Bible as a metaphor for bitterness or affliction. See also wormwood and gall (at wormwood).