When an ISTJ (Introverted, Sensing, Thinking, Judging) is mad, there are several signs and behaviors that you may notice. It's important to remember that each individual is unique, and these signs may vary from person to person. However, here are some common indicators that an ISTJ may display when they are angry:

1. Withdrawal and Silence: ISTJs are introverted individuals who tend to internalize their emotions. When they are mad, they may withdraw from social interactions and become silent. They may prefer to be alone and may not engage in conversations or activities as they usually would.

2. Increased Criticism: ISTJs have a strong sense of duty and responsibility. When they are angry, they may become more critical and nitpick about things that usually wouldn't bother them. They may point out flaws or mistakes in others' actions or decisions.

3. Blunt and Direct Communication: ISTJs are known for their straightforward and no-nonsense communication style. When they are mad, they may become even more direct and blunt in expressing their frustrations. They may not sugarcoat their words and may come across as harsh or insensitive.

4. Rigid and Inflexible Behavior: ISTJs value structure, rules, and order. When they are angry, they may become more rigid and inflexible in their behavior. They may insist on doing things their way and may resist any changes or deviations from their established routines or plans.

5. Increased Focus on Details: ISTJs are detail-oriented individuals who pay close attention to accuracy and precision. When they are mad, they may become hyper-focused on small details and may obsess over minor mistakes or inconsistencies. They may have a hard time letting go of these perceived errors.

6. Increased Need for Control: ISTJs like to be in control of their environment and prefer to have a clear plan or structure. When they are angry, they may exhibit a stronger need for control and may become more assertive or demanding. They may want things to be done their way and may struggle with accepting alternative perspectives or ideas.

7. Physical Tension: ISTJs may exhibit physical signs of anger, such as tensed muscles, clenched jaw, or a furrowed brow. They may appear more serious or stern than usual, and their body language may convey their frustration or irritation.

It's important to note that ISTJs may not always express their anger openly or confrontationally. They may internalize their emotions and may need time alone to process their feelings. It's crucial to respect their need for space and give them time to cool down before attempting to address the issue.