It varies. Some like them and some don't. It just depends upon the particular girl; obviously, ones who have piercings of their own are more likely to like it.
It depends on the girl. Some girls like guys with piercings and other girls don't. However, tongue rings are known to provide extra stimulation during oral sex, which can be a plus for some women.
I don't think girls like tongue rings on guy because personally I don't really find it attractive. I don't want to kiss a guy that has a medal piercing in his mouth. Also what if you have brasses then it could get stuck on your brasses. But I think some people might like it.
