The tag alias #80681 nipple_stud -> nipple_barbell is pending approval.
Reason: Self-explanatory, but even the nipple_barbell wiki page implies this.
Topic: Tag alias: nipple_stud -> nipple_barbell
Posted under Tag Alias and Implication Suggestions
Could have sworn there was already an active request for this one. Oh well.
Oh! I found it: topic #57088