Complaining is one of communication problems in relationships. Majority of us complain numerous times a day. It's perfectly normal and socially acceptable. We complain about our jobs, weather or commercials during our favorite TV series. Sometimes we complain to reduce our stress - after work we share a few sharp sentences with our housemates about our boss and we feel so much better. If the complaining process is not overused and we complain only about external factors (like weather, our boss, etc.) our interlocutor probably won't mind. It's not his fault so he's OK with hearing our complaints. This part is the bright side of complaining - it makes us feel better and is almost harmless (unless our interlocutor genuinely hates it). Unfortunately there is also the dark side ..
Complaining about our interlocutor
If we complain about our interlocutor things are totally different. Doing this, we blame him. We're holding him responsible for doing (or not) something and it makes us feel superior. We feel better but our interlocutor in most cases isn't feeling that good at the moment. Even if he admits his guilt, most times he doesn't really understand why we're complaining anyway. It's a rather rare situation that one understands why someone else is complaining about him. Things are valued differently, so even if something is the most important matter in the world for you, someone else would probably think why you even bother. It's how the world works, so thinking differently is quite naive. Besides, the damage is already done, so complaining won't change anything at all. It just makes the situation worse. Your interlocutor feels upset and (as being attacked) might start to defend himself. Some people are interpersonally intelligent ,so they admit their guilt and don't try to excuse themselves. The discussion is over and everything is going back to normal. Other people defend themselves and in most cases the person who complained attacks even harder. It leads to the inevitable prospect of further arguing. How to deal with that?
Make a request instead of complaining
The cure for the complaining disease is making requests instead of complaining. It's as simple as that. If something (in your opinion) is wrong with someone else's behavior, just ask him gently to fix it another time. It's also very good to explain to him why you think the behavior is wrong. If he can understand your motives, he would probably try harder to meet your needs. Besides, making a kind request almost never leads to an argument so it solves two problems simultaneously: you're avoiding a fight and informing your interlocutor about a problem, so the situation can be avoided in the future. One of the most important rules concerning explaining our requests is to never generalize about other person's behavior. Just stick to the facts and always talk about the behavioral patterns, never the person. If you will follow these guidelines you're probably going to finish the conversation just fine.
Real life example
My girlfriend is always upset when I am doing something not necessary with her laptop (like opening CD Rom drive without need). To a certain moment in time I genuinely didn't understand why she was upset about it. For me a laptop is just a machine, no feelings attached. If it breaks down I'm going to buy another one and pretty much everything is going to be fine. One sentence of hers made me understand why she's so concerned about her laptop. She said "if you would have been saving money to buy it as long as I had to, you would care about it as much as I do". After hearing that I totally understood her concerns about her laptop and since then I'm very careful with the device too. The problem is solved and we're both happy about it.
Remember, always make requests instead of complaining about your interlocutor and you will avoid many unnecessary arguments and make both you and your interlocutors life happier. Wish you luck with solving problems with complaining!