The phrase "beauty is in the eye of the beholder" is a paraphrase of an idea that dates back to ancient Greece, and it most definitely holds true. What one person considers attractive and appealing may not seem that way to the very next person who comes along. It's the base function behind what makes art, movies or music popular and it applies to tattoos as well.
Although people decide for themselves what's attractive or not, there are some written and unwritten rules for tattooing that seem to apply and if don't keep them in mind you run the risk of getting some ink that will have a very strong chance of drawing unsolicited feedback for the entire rest of your life and which might even effect things like dating or employment.
People at large still have a lot of hesitation, pre-conceived beliefs and negative reactions to just about any tattoo design if it gets placed somewhere that still carries a strong taboo. Backs of necks have seen this stigma lessen a lot, but heavy work that goes up the side or front of your neck will have the potential to be shocking. Faces still carry one of the strongest location taboos for tattooing, especially if you decide that a slogan across your forehead is the way to go. Some of the only people I know who've not had their life or work effected by a face tattoo are tattoo artists, so unless you want to go into that line of work, you might want to save the forehead billboard idea for after retirement.
Negative Imagery and Symbolism
Tattoos are viewed by many as something beautifying but if you choose negative imagery or symbolism, it may be something you just like to look at, but you will soon find that people will associate you with the designs. Scenes of violences, strong sexual imagery, obscene phrases and icons connected to notorious history might by symbolic to you but most people are going to view them as a true expression of yourself. These are the number one candidates when someone decides it's time to shell out the big bucks for laser removal. Most people who get a purposely shocking tattoo want to get a rise out of people, so unless you really want to court confrontation or possible gang profiling for the rest of your life, skip the nasty stuff.