Zealotive

[zel-uh-tiv]
Zealot + Relative
noun

1. A person connected through blood or marriage who exhibits far too much enthusiasm about some insignificant phenomenon to be considered sane.

Ex. Every year, Graham dreaded his annual Thanksgiving encounter with Aunt Doreen. She was by far the most tiresome zealotive of the family, known to blather on for hours about her fervor for rubber stamping.