Signs of a Demonized Person
These are just some of the common signs of a demonized person. They are listed here as a reference.
Please note: 
Not all of these signs have to be present for someone to be considered demonized; conversely, the presence of some of these signs does not necessarily mean the person is in fact demonized. However, if any of these signs and/or other sins (not listed here) are a recurring pattern in a person's life, I would suspect that this person has a demonic stronghold.

For example, it is possible for someone to be depressed (for instance, at times of mourning the loss of a loved one, etc.) and NOT be demonized. However, if a person has a recurring problem with depression, this is a spiritual problem. You should always be careful and sensitive when evaluating whether or not demons are the cause of these conditions in a person. As always, rely on the Holy Spirit for discernment!

Confused or disordered thinking: loss of touch with reality, hallucinations, delusion, disconnected speech.
Obsessions: absorption with a subject or idea - compulsions - uncontrollable urges.
Inability to cope: with minor problems - with daily routines of life in general.
Difficulty in making or keeping friends: poor social skills - isolation, a withdrawal from society.
Patterns of failure: at school - at work - in sports - in personal relationships.
Prolonged or severe depression: suicide threats or attempts. Obsessed with death and things of darkness.
Immaturity: infantile behavior - over dependency toward the mother (excessive clinging as a child - continuing into the teens and twenties) - fails to keep pace with their peer group.
Physical ailments that do not run a typical course or fail to respond to medical treatment.
A neglect of personal hygiene (unsanitary surroundings) -- OR an exaggerated concern for order and for cleanliness.
All addictions: Alcohol, Cigarettes, Drugs, Porn, Etc.
Constant anxiety and worry: phobias - feelings of being persecuted or threatened.
Muted, "flat" emotions or inappropriate emotions (sharp, inexplicable mood swings - silliness at serious moments, unpredictable tears). Roller-coaster emotions.
Negative self-image and outlook: "inferiority" complex - feelings of worthlessness.
Extreme aggressiveness (combativeness, hostility - violence, rage) Always angry. Competitiveness and self-assertion - refusal to confront, avoidance of argument).
Lack of zest and enthusiasm: listlessness, sadness, and mood habitually "down" -limited or missing sense of humor and laziness.
Unforgiveness, bitterness, resentment.: Towards other or self. These 3 lead to anger, hate, rage, and internal torment.