Demonic refers to behavior or situations possibly influenced by demons, such as unexplained evil actions or emotionally charged extreme anxiety. Demonic manifestations can occur in groups of people as well as isolated individuals, and can arise in what appears to be pure chance. Even young children can occasionally initiate demonic deeds without any rational explanation.
Elements of chance or uncertainty, as found in gambling and games like football, seem to enable demonic influences to thrive.
Entire nations, particularly when ethnically homogeneous as Germany was in the 1930s, can become demonic. Dogs and other animals might also occasionally become demonic, and thereby create dangers.
Some atheists deny the existence of evil and thus deny the possibility of demonic conduct. But even then there are popular secular uses of the term, such as "demonic laughter" in a movie.
The blockbuster movie The Exorcist famously depicted demonic conduct, supposedly based on a true story, The movie broke the record at the time for box office revenue and was upsetting to many who saw it.