Testosterone makes you angry. This is probably the most common myth about T. The reality is that there’s no concrete evidence that high testosterone levels cause anger and violent outbursts. In fact, the opposite might be true; low testosterone, not high T, is what causes anger and irritability in men. As discussed above, having low T levels has been linked to depression in men and it just so happens that two of the primary symptoms of depression in men are increased angry outbursts and irritability. So if you’re chronically angry, you might be depressed, and you might be depressed because you have low T. As I mentioned above, I became less moody and irritable during my experiment, which I attribute to the boost in my testosterone levels.
The second theory is similar and is known as "evolutionary neuroandrogenic (ENA) theory of male aggression".   Testosterone and other androgens have evolved to masculinize a brain in order to be competitive even to the point of risking harm to the person and others. By doing so, individuals with masculinized brains as a result of pre-natal and adult life testosterone and androgens enhance their resource acquiring abilities in order to survive, attract and copulate with mates as much as possible.  The masculinization of the brain is not just mediated by testosterone levels at the adult stage, but also testosterone exposure in the womb as a fetus. Higher pre-natal testosterone indicated by a low digit ratio as well as adult testosterone levels increased risk of fouls or aggression among male players in a soccer game.  Studies have also found higher pre-natal testosterone or lower digit ratio to be correlated with higher aggression in males.