The first thing you should do if you don't like a tattoo is avoid despair. There are some solutions to your problem, none of which involve a flensing knife. By keeping a cool head about the issue, you can reach a workable solution which will hopefully make you happy, and make the disliked tattoo a joke or funny party story, rather than a sore subject.
When you consider a tattoo, take the time to think deeply about whether or not you really like the design and if you will be happy with it in 30 years. Find a tattoo artist you like and trust, and work together on an image which pleases you both, considering issues of design and placement to ensure that it will be exactly what you want. While there are options to pursue when you don't like a tattoo, it is better to get one you like in the first place.
There are a number of reasons to be dissatisfied with a tattoo. Some people, for example, get tattoos which are important to them and later undergo lifestyle changes; gang tattoos are an extreme example. In other cases, you may get one which is poorly applied, and be unhappy with the outcome. Most rarely, people are forced to get tattoos, in which case disliking it is certainly understandable.
If you don't like a tattoo because you think it is of poor quality or it needs work, you should go back to the shop where you got it done. While you may not want to work with the same artist, the staff at the shop will often work with you to fix the design for free, as shops like to keep their customers happy. In some cases, a gentle touch up will resolve the issue, while in other instances you may need to consider a coverup. If the shop will not offer compensation in some way, you may want to complain to the Better Business Bureau or a similar organization.
When you don't like a tattoo because it hasn't aged well, you have a few options. Modifying it is the easiest and least expensive. Find a tattoo artist who works in a style you like and is willing to do coverups or modifications, and talk with that artist about your options. Depending on the design and inks used, you may be able to turn a hated design into a beautiful new one. As you design a modification or coverup, take the time to make sure that you genuinely like it so that you don't repeat the experience in 10 years.
Tattoo removal is also an option. It can be accomplished in a number of ways, and the technology is improving all of the time. If you believe that removal is the best option for you, talk with several experts about your specific tattoo to find the method which is most appropriate for you. Former gang members can often receive tattoo removal treatments for free, through community organizations. Some artists will also do coverups on former gang members for free, incidentally.
If you are the victim of a forced tattoo, the same coverup and removal options apply. Some tattoo artists will donate their time and skills to your cause to create a coverup, and victim's compensation funds can help you pay for a coverup or removal, depending on your feelings about it. You may also want to consider a third option: some victims bear their tattoos with pride and as a social commentary, as many Holocaust survivors did.