Nothing pisses me off more than someone who thinks they can get along with everyone. They think they're being kind, and don't see how insultingly arrogant it is to sand yourself down and expect the other person to do the same.
Humility, and not the fake kind where it has to be asserted through sycophantic self-deprecation. I like people who are slow to judgement and who think patiently before speaking, who recognize their own virtues and the virtues of others.
The reason "detective" is a profession and not just a word for an observant person is that you have to be an asshole. "Professional distance" is the polite term for it. A nosy busybody that asks questions that make you cry and roots through your garbage and breaks into your house and stalks you. Nobody would treat their friends the way a detective has to treat people, or at least nobody should. When this is your job - your real job, not a one-off dalliance - anybody could become a person of interest, and that means you have to be prepared to do this to anybody.