A person who has been traumatized may become fearful of the kind of person who hurt them—men, women, people of a certain race or nationality, members of law enforcement, the government, etc. There can be other causes, such as an irrational fear resulting from a mental health condition or being brought up to be afraid of certain people groups. Regardless of how it arises, this goes beyond a simple trust issue; a fearful mindset toward certain kinds of people will restrict the character's options and who they're willing to interact with, limiting them in many ways.

Avoiding places where the people they fear are likely to be
Becoming anxious when an opportunity arises that will bring the character in contact with the people they fear
Speaking disparagingly about the people
Gravitating toward media that affirms their bias (watching movies with "those kinds of people" as the bad guys, subscribing to podcasts or YouTube channels that affirm their beliefs, etc.)
Their demeanor changing when someone from that people group enters their space (falling silent, not making eye contact, watching them furtively, becoming confrontational, leaving the room, etc.)
Showing signs of physical distress when faced with the people they fear: going pale, extremities trembling, accelerated breathing, clenched fists, etc.
Crossing the street to avoid close proximity to those people
Taking a work-from-home job that ensures the character will never run into the people they fear
Surrounding themselves with their own kind of people (hanging out with other women, or the character immersing themselves into their own culture, for example)
The character worrying so much about running into those people when they go out that they become homebound
Feeling endangered when those kind of people are around
Others viewing the character as ignorant, biased, or discriminatory
Strained relationships with family members because of the character's ideas about certain people
Speaking out against that people group in an effort to protect or inform others