A person who will only wear clothing that is hideously expensive and bears the 'right' tag or label in the belief that she (it is mostly she) is a better person for doing so. Often tag hags are also fag hags for some reason.
"She's such a tag hag. She wanted to wear my Versace even though she hates it!
A teenage girl who insists on tagging herself in every Facebook photo of herself she can find...IF it's flattering.
"OMG! Donnie just uploaded 4,876 photos from our summer at Seaside! It's going to take me FOREVER to go through all of them to find the good ones of ME!".....such is the Plight of the Tag Hag.