Most of the things I'm good at (basketball, tennis, piano) are common around the world. Since I'm not elite in any (or else would do it for a living) my world ranking has a looooooong list ahead of me. I'm a CPA but there are accountants across the globe. Localized talents such as knowledge of LSU football are not considered but less popular games such as foosball would be. Will have to think longer about this for myself. Popped into my head when I told my 7 yr old last night that Lebron was the best basketball player in the entire world. He asked what my ranking in the world was and I said not great. He asked "Like #100?" and I said more like # 1,000,000.
I haven't played ping pong in about 20 years and I have no idea what my world ranking would have been. Pretty bad I'm sure compared to the Chinese and Koreans. I used to play pretty regularly against a few players who were ranked in the top 10 in the state of Louisiana and I held my own pretty well, winning as much as I lost.
Probably wakeboarding or barefooting. I was good at both and they're relatively obscure. Top 1000 in both most likely. Maybe top 500 in wakeboarding.