Location: Berlin, Germany
Word or Expression: der Giftmischer
Closest English Translation: chemist, troublemaker, stirrer
Literal Translation: poison mixer, preparer of poison
From what I gather, this can be really used to call someone a poison mixer, someone who in fact tries to poison other people. It is also apparently used as a way to call someone a troublemaker.
das deutschsprachliche Projekt Teil 2 