I assume you mean ‘hair on fire,’ which suggests a move done in a panic. “Pants on fire” means the subject is lying.

They fired him for lying. I think GP meant what they said, which is that what he was doing was blatantly lying, rather than whatever softer interpretation can be made for "not consistently candid in his communications".

Actually I did mix up “hair on fire” and “pants down”. Fortunately, “pants on fire” still works in context.

Ok, but it fits so well with "liar, liar, pants on fire" and their reason for dismissal.