sick in the head

Translations
не в своем уме
Anyone who harms animals for fun is sick in the head.
Любой, кто причиняет вред животным ради забавы, не в своем уме.
Definitions
A colloquial expression used to describe someone who is perceived as mentally unstable, irrational, or having disturbing thoughts or behaviors. It can be used seriously or as an insult.