Why? Because giving someone the satisfaction of knowing you don't like him is the equivalent of handing over all your power. This individual now knows how to push your buttons and will use the fact that he makes you uncomfortable as a weapon to see what reactions and feelings he can provoke. Please don't mistake this advice for being a pushover. I'm saying at some point, one must learn to deal with even the most repulsive people constructively. No matter what occupation you work in- even if you work for yourself you'll still come across annoying and difficult people. It's not how you handle them, it's how you handle yourself that will make all the difference. If that means smiling in the face of someone you hate just long enough to do a business transaction, so be it.
Everyone has something to offer, even worthless people. You never know when you might need someone. That person you just insulted might be the jump you need when your battery dies. That person you just got into an argument with might have some important information you need later on down the line. You don't have to like or have an ounce of respect for anyone, but it pays to be diplomatic. Granted, most people will have enough common sense to pick up on the fact that you're not too fond of them- and that's okay. However, it's not necessary to rub it in their face.
On another note, there's always something going on behind the scenes that you're unaware of. Until you know every detail of a person's life try to refrain from forming judgements and losing your patience. You'll thank yourself later.
