Some people choose their tattoos based on what a lyric, expression, object or memory means to them, while others get tattoos simply because they just want them. Getting a tattoo of a slice of pizza doesn't have to come with a long-winded, sentimental story of how you used to roll out pizza dough with your grandmother (although that's nice). Some people just get a slice of pizza tattooed on them because they just like pizza, full stop!
However, there are some tattoos that really make you wonder what was going on with that person when they chose to get them. Of course, checking for spelling and grammatical errors is key, being sober when you go to the shop, and making sure that if you're going to get a tattoo in a language you can't speak that you really know for sure what your tattoo means. Still, sometimes people are lucky that have a wise tattoo artist to sway them away from making a regrettable permanent choice.