If you can't think of anything you would want, why are you trying to push yourself into getting one? Why not just let the idea sit in your subconscious until one day a picture becomes such an obsession that you can't imagine your life without that tattoo, and then take the plunge?
A funny comedian, Daniel Tosh, says why don't you just get a tattoo that says "I'm dumb" so that way whenever you forget why you got a tattoo in the first place, you can just look at it and know!
I have a pretty big tattoo, but I wanted it bad, and I waited until I was 29 to get it, so I knew I could handle it. PLUS I got it somewhere that I can cover, so in case it ever becomes something less than flattering, nobody has to see it. NO NECK OR FINGER TATTOOS!!!!