Not much else to say. When someone snaps at you, writes a bad comment on your Instagram post (not big enough to have that happened to me yet), someone is tricky to be around with, or whatever...
..remember..
..they are trying their best and might just have a really rough day/week/month/year/life.
Not saying that it isn't their responsibility to take care of themselves too, nor am I saying it's your job to help/fix them, nor is it that you should feel like you can be pushed over/you need to constantly sacrifice and take a hit, just that sometimes a little sympathy, letting things go, or offering a little gesture goes a long way.
Be kind.