Scenario 1
You get off on the wrong foot with a new coworker.
They ask you for help responding to a customer inquiry, but you refuse to lend a hand because you are working on a tight deadline and don't want to waste time. There has been tension between you two ever since, and now you need their help on a project, but they're not being very responsive
Proposed Solution
Go own it! Find an appropriate time to walk up to them and say,I understand that we got off on the wrong foot. My apologies for that. What I'm trying to resolve is X. Can we have a conversation about that.
Regardless of who the conflict is with - an employee, your boss, etc.they'll think more highly of you if you demonstrate self-awareness. The conversation may be awkward, but that's better than a tense relationship that could last years all because you got off on the wrong foot
Scenario 2
You're frustrated because your colleague in France keeps messaging you at 5am (your time). They send you seemingly urgent requests when you're sleeping or just waking up, and you're sick of being bombarded with 11 requests before you've even sat down at your desk. You get the vibe they don't like you very much and you don't know how to approach them.
Proposed Solution
Avoiding confrontation is making your situation worse, not better! Schedule a time to chat with them via phone or video call.
Uncover the root of the problem by asking questions "Is there any particular reason you send me requests before I'm up? Am I responding to you too late?
Once you understand why they're doing it, you can help them articulate their needs. Maybe they send you 11 messages at 6am because that's right before their lunchtime, and they don't want to forget their questions when they go on break.
Now figure out a solution that works for both of you. Can they send themselves a reminder on Slack to ping you with their questions when you're at your desk? Can you just ignore their messages until you clock in now that you understand they're not time sensitive? Should you schedule a morning check in to go over these requests in real time rather than via message.