Everyone is reasonable when you understand their reasons
This is a gem I have mentioned before through the blog and was given to me by a good friend. The power here is in realising that people are rarely acting to deliberately damage or frustrate you. Rather they likely have different reasons for action than you, and these may contradict your hopes for a situation. If we can take a step back and gain perspective then we give ourselves opportunity to consider the motivating forces behind others actions. If we can realise these then it will likely make us feel less tension and enable us to calm our emotional responses.
Do not assume malice where you could also ascribe busyness
When you feel hurt or any other negative emotion from a situation it is likely that your mind will jump to a conclusion that the other person(s) involved are in some way out to get you. This is due to our hard wiring and our innate ability to try and identify threats. The reality is that very few people are intentionally out to do us harm. Often they are just busy and don't fully think things through, you being hurt is an unintended side effect. In situations where you do feel negative emotions ask whether they are likely intentional or whether they could be explained away by busyness, incompetence or any other, more useful, explanation you see fit to use.
Imagine that everyone is simply trying their best
This phrase is the most recent in the list for my own use and it is has proved challenging and effective in equal measure. Effectively you have to ask yourself whether life would be better if you just assumed that everyone was just trying their best with the resources they have available to them. Whilst you may snort and declare that this certainly isn't the case you are missing the point! This isn't about the reality of a situation, it is manipulating our beliefs about the situation to lead to a more positive effect. If we assume that others are trying their best it helps foster compassion and empathy. We don't personalise things and, as a result, we remove tension and help develop deeper relationships as a result.
Whilst these phrases aren't a panacea for all relationship woes I hope that you will find them useful to smooth over situations where you feel you have been slighted and move past petty differences that are blocking your relationships. Simply read through them or mentally remind yourself any time you feel frustration creeping in. I assure you that you and the other person will feel and do better as a result.