Terran behaviour is fairly unpredictable and varied. There is seemingly no set psychological pattern that humans behave to, as all human individuals are different. Some societies of humans tend to focus greatly on resource exploitation and greed, whilst others live to preserve nature and life. Other species sometimes describe humans as violent and irrational, but the truth is that there are just as many humans who pursue peace as there are humans who seek out to do harm.
So in those senses, humans are perhaps the most adaptable species for emotion and usual conduct. Humans are quite social and at times very curious about most aspects of life. Humans show greater interest in understanding things about the universe and how it works than most other known species, though they are not always as set on one goal as the other species. The typical human-being has at least two or more set goals for his/her life, since humans as a whole tend to dream for greater things far more than other species do.
Human decisions are based mostly on situation and consequences of the moment, and those decisions are not always so ideal. Humans will often make decisions without gathering all the facts first, and they would for the most part trust their feelings and their guts than logical solutions and thoughts. As such there is perhaps some truth in humans being irrational and, according to some species, stupid. But humans themselves will consider at least the first trait a useful one, as sometimes one must simply just "jump the gun" instead of gathering all the facts of a situation.
It would also seem that humans prefer the presence of their own kind over others, and are often either distrustful or nervous when in the presence of another species. This depends mostly on what planet the human hails from, as there are many planets, particularly bordering alien-controlled systems, where humans have grown accustomed to mingling with non-human entities.