God damn you are taking this seriously. Obviously that is a superficial ranking system I made up in 30 seconds as a joke.
Although, you know, if we are going to take this super seriously, how many girls do you know that had tongue rings? Were they generally pretty slutty?
A tongue ring improves oral performance. Because of this, men will associate a girl that has one as a girl who likes to use it. Women realize men will make this connection. Some of them, knowing men will make this connection, choose to have one anyway. Maybe they like the attention, maybe it helps them feel a little bit sexy and more confident, maybe they just like piercings. But girls I know that have tongue rings I would say are on average more likely to blow you than a girl without one.
Every girl I've ever known with a nipple piercing has pretty much been of the looser variety if you'll excuse the term, and they like to show them to people.
So really, because of the subconcious associations people make between body piercings and sluts, girls who are more sexually liberated tend to have them more. Its an interesting causeXeffect relationship.
The only thing wrong with this is that being a slut is considered a negative thing be today's society but only if you are a girl. If a guy had a dick piercing, you would probably think he really likes sex, but there just wouldn't be any negative connotation with that. And thats a problem with society, not me. All I know is that girl I just met at a party who's wearing a fuzzy tongue ring that can be turned on to vibrate is more likely to blow me than the girl wearing an amish get up with no body jewlery.