A pantyfan is someone who wets their panties over the person or persons they are fanning over. Alternately, they are willing to throw undergarments on stage. This term is most commonly associated with musician Imogen Heap, but can be used for all sorts of things including but not limited to: musicians, films, stores, electronics, and breakfast pastries.
You do not have to wear panties to be a pantyfan.
The Hideaway Team's Elwoood is Imogen Heap's #1 pantyfan.