According to a 1994 study, people who are angry tend to make judgments based on shortcuts- as opposed to evidence.
Anger, in particular, can short-circuit our ability to think through things, and increases our reliance on "heuristics" or mental shortcuts.
Psychologists concluded that:
(A)nger is an emotion that tells us there is a need for quick action, and thus increases heuristic information processing. Thus, when we are angry, we tend to use mental shortcuts to decide whether an argument is right.
One more interesting finding in the same study was that angry people tended to fall back on stereotypes- a kind of short-cut thinking which doesn’t rely on actual evidence.
Yet another type of mental shortcut that people use when they are angry is stereotypes. In the same study by Bodenhausen and colleagues, angry participants were more likely than sad participants to find the same set of evidence as indicative of guilt when a criminal defendant was named as "Juan Garcia" as opposed to "John Garner." Again, the angry participants went with the heuristic-- in this case, the stereotype of Latinos as criminal - rather than focusing on the evidence per se.
So, as the study suggests, people who are angry tend to be more reactive and tend to think less analytically. Experience seems to reinforce that view. All of us understand the idea behind the phrase, “And then he saw red.” The study confirms most of us already knew: anger is a blinding thing.