Stay calm. The most important thing you can do is to stay calm. Taking on the persona of a loud, irate jerk who verbally abuses the customer service representative and makes other customers feel uncomfortable never helps and is likely to make your situation worse. Even worse than getting poor customer service is getting arrested for harassment or disorderly conduct.
Be sure you have a case. Know the business's policies and/or the law that surrounds the issue you want to complain about. If you don't have a solid basis for your complaint, then you are asking for special consideration -- which you may or may not receive, depending on the business and your value as a client.
Speak with a decision-maker. Most front-line customer service reps have very little decision-making power so it would be best to summarize the situation and discover whether or not the person you're talking to can help meet your goals. It is almost always preferable to speak with a supervisor (who are trained to resolve larger issues) and is doubly beneficial to the customer service rep who needs to keep his/her call time to a minimum.
Write down your goal. This should be something well-defined: "replacement cushions" or "partial credit" or whatever. If your goal includes "revenge" you have officially made yourself a loser. Take a few deep breaths and calm down, or you'll quickly be classified with the "nutballs" who have an axe to grind and your (legitimate) grievance will be dismissed.
Come prepared. Bring your product brochure or the store's customer-service policy with highlighted points on it. It undermines your case completely for the business to point out a written requirement that you didn't notice or comply with. If it's a legal issue, look up the pertinent statutes using your favorite search engine and print them out. Find a telephone number for the business's regional or corporate headquarters, just in case you need it. State the problem clearly. Your new clock radio is so bright it keeps you awake at night. Your toaster burns your pop-tarts even on the lowest setting. You bought a trampoline and when you opened the box, not all the parts were included (be prepared to state which parts are missing).
Communicate your goal. If what you want is a replacement, state this clearly. If what you want is a refund, make this clear. The business cannot satisfy you if you do not know what type of relief you expect. Explain your situation simply, without embellishment. Tell them how much you shop at the store and about any rude or unreasonable personnel you've encountered.
Give the business three chances to correct the problem at the store level. This usually follows a chain of command: Customer Service (or cashier), Service Manager (or supervisor), Store Manager. IMPORTANT: write down the first and last name of every person you speak to -- ask if the name is not on the employee's badge. No matter how frustrated you feel, never yell at cashiers.
If the complaint cannot be resolved at the store level, take it to a higher level. Calmly tell the store manager that you will resolve the situation with Corporate and find the nearest phone. If you have a cellphone, stand just outside of the store to place your call. As above, explain your situation without embellishment. You will be given instructions about what to do next -- email a certain person, send a copy of your receipt to a certain address, etc. Listen to the instructions carefully (write them down if possible) and follow them exactly.
If no corporate structure is available, or if Corporate also fails to satisfy you, report the business. Most legitimate businesses will respond to a Better Business Bureau (BBB) report. Find the BBB that is local to the business you are complaining about. File an online complaint. Wait a few days to see whether the business responds. If no response is forthcoming within fifteen days, file a RIPOFFREPORT.COM report to let others know your experience.
Go to the Federal Trade Commission website and file an FTC Consumer Complaint. It's a possibility your report will be used in an investigation.
Find websites that are reporting similar issues. Add your comment to the discussion. You never know; an attorney may be scouring the web for a class action lawsuit.
Describe your situation on your blog. Remember, don't defame the business and remain truthful without embellishment!
Protest physically. Round up as many friends as you can to help you protest. Make your signs EXACT and non-defaming, like "X sold me a defective trampoline" or "X overcharged me and will not refund my money." Do not use signs like "(expletive) X" or "X breaks the law." If you know anyone who can help, let your contact notify a local newspaper or TV station about your protest. Be sure to check the local laws concerning picketing first. These laws vary from municipality to municipality. In most cases you must obtain a permit to protest. Permits are generally issued at City Hall.
Get a lawyer. This should be your last resort, but if you have exhausted all the other options, still haven't gotten a proper resolution, and aren't willing to give up, then find an attorney.