1. An untoward fixation with Hillary Clinton, either from political opponents or from overly enthusiastic supporters.
2. A shameful state in which one is ideologically opposed to Hillary Clinton, yet secretly finds her attractive.
“That right-wing blogger keeps spewing lies about Hillary. He really has a Hillard-on for her!”
“I’m so tired of you telling me how great Hillary is. Dude, lose that Hillard-on!”
“The aging GOP fundraiser had to turn away from the TV screen every time Mrs. Clinton's face appeared, lest he reveal his shocking Hillard-on.”