What happens when two people have a dispute? The Torah describes the legal process: "When two people have a dispute and they approach the court and they judge them; the court vindicates the righteous one and finds the wicked one guilty. If the wicked one deserves lashes the judge should bend him over and hit him according to his wickedness. He shall hit him forty times, no more, lest he hit him an additional time and your brother will be degraded in your eyes" (Devarim 25, 1-3).
Rashi points out the obvious question. Three times the pessukim refer to the one found liable as wicked and immediately thereafter the Torah refers to this same wicked man as your brother. What changed that the Torah ceased to refer to him as a wicked person and chose a more positive term? What changed is that he received forty lashes. Once he received his punishment he is no longer wicked. He is your brother - no different than any other Jew.
Rav Wolbe (Shiurei Chumash) notes the great difference between the way the Torah deals with a wrongdoer and the customary way a court of law deals with an offender nowadays. When a criminal is caught, he is brought to court and they open a file. Even after he receives his punishment, his name is forever tainted and he is black listed as a convict. Additionally, on a social level it is difficult for him to regain his former stature and renew his past relationships. In the world of Torah law this is not the case. As soon as the punishment has been meted out, the offender becomes your brother in every possible way.
Moreover, Rav Itzele Blazer would say that from a Torah view, even a thief has to be dealt with in a respectable manner. If he has the money to repay what he stole, he must make restitution, and no one will know what occurred. This differs greatly from the way thieves are dealt with in contemporary society where as soon as someone is caught, his crime is publicized, which can ruin his entire life. The mitzvos bein adom l'chaveiro are not limited to those completely righteous. The halachos apply even to criminals, and if so, they most certainly apply to your neighbors and colleagues. Even if you do not see eye to eye with them on a few or even numerous occasions, this does not absolve you from acting toward them in the same way that you would act toward your close relative. Although the difficult person is not your blood relative, he is still your brother!