1. to engage in thought processes that lack logic, reason, or sound judgment; to reason without rational basis
When he's angry, he tends to think irrationally and makes poor decisions.
Quando está com raiva, ele tende a pensar irracionalmente e toma decisões ruins.
2. to form conclusions or beliefs based on emotions, bias, or prejudice rather than evidence
People often think irrationally when they are under stress or fear.
As pessoas frequentemente pensam irracionalmente quando estão sob estresse ou medo.