I'm a young adult, and both of my parents come to me when they want to complain about the other. (They are married, but their relationship hasn't been on good terms for a couple of years.) I don't want to take sides or talk badly about either one behind their backs. How can I explain this without hurting my relationship with them?
What's going on is called "triangulation". In a dispute, sometimes one or both of the parties will attempt to draw a third party into the dispute to make them feel like their position is stronger. Often they will use your relationship, guilt, or anything available to them to get you into the middle of their issue.
The key here is to recognize when this is going on, which it sounds like you have done. One thing I've seen done, especially in the workplace, is to say, "I'd rather not talk about someone when they can't defend themselves." That quite often draws that conversation to a close.
With a married couple, that's harder because feelings run stronger. To keep out of the middle of this will require a lot of determination on your part and willingness to not accept guilt that will be thrown at you.
First of all, when they start talking about the other, stand your ground. "Mom/Dad, I'm both of your child. I realize things are hard between you two, but I love you BOTH and can't get in the middle of this." "Mom/Dad, I understand you're having a rough patch. I'm here for you but let's talk about how this affects you and not talk about the other person." "Look, this is tough on all of us. By trying to get me to choose sides, you're just making this tougher on me. I love you both and can't take sides in your issue." And be firm.
When you hear the "if you really cared" or "don't you think that", the response needs to be firm as well. "if you cared about me, you wouldn't say 'if you cared'". "Don't I think that...? What I think isn't relevant. It's not happening to me; it's happening to you". You can love your parents yet still avoid being drawn in. And if you can't avoid being drawn in, a month or two of stepping away may be necessary to keep your sanity. Remember this: you're their child, not their therapist.
If you have access to a minister or trained marriage and family therapist, a visit or two would be good for you. They can help you learn more about triangulation and how to stay out of it, as well as give you more tools to deal with this. If your parents' relationship is bad and not getting better, a therapist can help you deal with the next stage of their relationship, whatever that may be.
The best way is to be straightforward, and assertive.
You know I love both of you and it hurts me to see you fighting. I will listen to both of you and not take sides and it is not fair for you to ask me to do so. You are my parents, please don't put me in this position.
This starts out in a positive way, then plainly states the effect it has on you, then sets boundaries. You are telling them that you love them but this behavior is out of bounds. You are also reminding them of your roles in the parent/child relationship.
Once grown up to full adulthood and maturity, a problem between two people should be
solved by the two directly-involved people by talking to each other
Addressing a third party in day-to-day arguments sounds as childish as the case when two little brothers fight and one of them screams "Mooooom!!! Bob is being mean to me, tell him to stop!". This is also worsened by them addressing a person who should be and is too close to both parents.
First, they need to prove their adulthood/maturity by learning to sit down and talk directly to each other and staring into each other eyes. If that fails, address someone definitely more external than a son/daughter.
That explained, in my opinion your answers could be:
Just be straightforward and declare your point of view.
Look mother/father, I love both of you equally, I can't get involved with this - I'm too close to both of you and this fighting upsets me.
I'd suggest that they take this dispute to someone who is truly impartial and can mediate properly.
Mom/dad, please, stop being childish, this is not the way to deal with problems at your age: every time you argue you act as two little brothers [etc. see above]
a combination of them both
I'll be very straightforward. Having my parents divorced from age 4, I have been in that situation more times than I can count. It took its toll on me, but I'm ok now. What I mean when I say it took its toll, is that I learned to answer them truthfully without feeling like I was being disrespectful, because in fact what they were doing was disrespectful towards me. Firstly you need to remember that family isn't always a good thing, and the worst part is that you don't get to pick yours, so you might be stuck in a pretty bad situation when you are born. Therefore, analyse your parents as you would analyse any other person, and think whether the situation you're stuck in would be acceptable if your parents weren't actually your parents.
In my case, it wasn't, so all I said was:
Listen here. I DON'T care about your interpersonal problems. That's for you to solve. You are hurting ME and I don't deserve this. Learn to behave yourselves and treat eachother like adults should.
They then realized they were failing as parents, since they were hurting me, their child, and stopped doing that.
Previous attempts to tell them to stop doing it softly like others have suggested resulted in me getting tricked into a trap where they would either tell me I didn't love them or that I should go live only with my other parent or anything like that. Parents at any age have the upper hand in the power relationship with their children, therefore they can use that power in their favour, you'll never win if you let them have a chance to put themselves first instead of you.
Always keep in mind that, ultimately, you are the person that is the most important in your life, so you should be egoistic sometimes if that means saving yourself from harm.
I would recommend not only to stop taking sides, but stop listening to them complaining about the other person.
Listen, I am your child, you are my mum, I don’t want to know about your issues with dad, nor can I help you to resolve this. Being told such things is putting me into the position of a referee, a psychologist or a judge, but I am none of this but your child. What do you think about what I just said?