Well, I have several tattoos and my wrist hurt the least. In fact, to me, it didn't hurt at all. But pain is realative..if this is your first tattoo it might hurt a lot.
First thing to consider..WRIST tattoos CAN BLEED OUT. Meaning in just a couple years (or even one) the ink can smear out. It is better if you put the tattoo a bit above your wrist. The thinner the skin, the more likley it can bleed out. It doesnt happen to anyone (My feet are tattooed, and they haven't bled a bit)
Things like sunscreen and proper healing care will also be factors in that.
But yes; wrist tattoos are hard to cover up. Don't EVER assume you will have a job that will allow tatoos. THINGS CHANGE!!!!!!!!!!!!!!! (A lil hypocritical from me, lol)
But if you do, you can buy dermablend to cover it if it is small.