1. Indicating ownership:
Person 1: "Oh my gosh, that sweater is Hilaryous!"
Person 2: "Oh, okay, I was wondering to whom it belonged. Hilary must have left it here, the last time she visited."

2. Pertaining to idiosyncrasy of the Hilary-person:
Person 1: "You know that thing Hilary always does, when she leaves social gatherings without notifying her friends? She seems to catch a thrill from gaining MIA status; it happens nearly every weekend."
Person 2: "Oh yes, that thing. It's never funny but so Hilaryous all the same."

Hilary Clinton is hilaryous!

When Hilary vote for the war in Iraq it was hilaryous.