Don't do it to please or pick up some girl!!! There is one thing in life that you can count on, is change. What may seem like a permanent, stabile relationship at one point in time, may fail a couple years down the road. So girlfriends (or even wives I hate to say) is a pretty dumb excuse for a tatoo.
The only semi-decent reason I've seen for a tatoo was a NFL player who recently explained that his tatoos were in honor to the women important in his life when he was growing up, mother, grandmother, aunt, older sister etc.
Even the military is coming down against tatoos. The Marines recently implemented a fairly strict anti-tatoo policy. So even groups that in the past were closely associated with tatoos, are now coming out against them.