Problems. Everyone has them, even if you don't know about them. Some may relate to a person's family or friends, while others are internal struggles people can never see. No matter the contents of the problem, they exist, and they affect people in all different ways. How people react to problems they face help shape who they are and what life they want to live going forward.
Struggles are universal, but their impact is not. A common practice of people dealing with issues in their life is to be bitter or angry at life. This reaction to life problems is a problem within itself, and it's time people realize that your problems don't excuse your poor attitude in life or your crappy behavior.
You have no excuse to be a mean person just because you have problems. Every person on the planet has problems, and it's your responsibility to learn to cope with them. There are thousands, if not millions, of coping mechanisms out there when you're struggling-- so don't take out your negative feelings out on others. The world is already filled to the brim with negative feelings like anger and bitterness; there's no need to add to that just because you got dealt a bad hand in life. Negativity spreads like wildfire, so you acting out over your own problems will just start a chain reaction of people being negative.
I've faced plenty of struggles in my life, but I don't let that hold me back from being a good person. I get to wanting to be angry because it's easier than dealing with your emotions, but it's not the right way to live your life. Living your best life means being the best person you can be even if your life can be horrible. I don't let my struggles, past or present, stop me from being nice and kind to everyone that I can. I don't let myself waste energy being angry at life when I could be out doing good for the world. That's what people should learn to do.
Stop excusing your actions with your problems; you need to take responsibility for how you act whether your life is a mess or not. You are choosing to expel negative feelings and behavior out in the world because you can't cope. That just makes things worse for others, So if you can't cope, don't put that on others. It is every individual's responsibility to take care of themselves and how they act. Learn how to be good even when life isn't. That's the goal, so aim for it.