What kind of person are you if you have bad feelings but never act on them. Not in a really bad way, but say you don't like someone but just get on with them to keep the peace and not hurt feelings. Are you a bad person for having the bad feelings or are you a good person for not acting upon the feelings?
People I don't like I can't actually be arsed with so I'm not even interested in a confrontation or argument to them, I just don't care enough about them or their opinion to bother with them. So I don't act on my feelings if I dislike someone as I just don't act period. You should always pick your battles and make sure it's over something you actually care about.
I agree with CD, why rock the boat when you don't have to. You can't like everybody but you obviously like others as you want to keep the peace, just avoid as much as you can.
Neither, everyone has a hunch or a feeling about someone at some time or another. I just find it easier to avoid them or keep out of their space. In the workplace it's easier to get on with your job, act naturally with them and keep your own counsel, no point in having a simmering enmity with someone.
I've done both the 'Caine Dingle Charm School' approach with people in the past and the more mellow me now who just grins and bears them and rubs along with everyone else, and believe me life is pleasanter and easier now, and I think I'm a nicer person for it, usually.
pick your battles... mostly treat the small stuff for what it is... but if you find something really gets to you there is no harm in saying I feel really angry/unhappy or whatever about what you said/did and I'd prefer it if you would not do it again/ or whatever course of action you prefer... they might go off on one but stay calm you have made your point listen to their response and walk away