Used with humor, as a simple statement, in a conversation when you strongly disagree with the majority. Originally a French term used in psychiatry to describe a mental disorder in which two or more associated persons share the same delusion. In other words, you are saying "The two of you share the same delusion." Translated "madness between two."
Two others state "G. Dub is an excellentpublic speaker." In your disagreement, you respond with "Folie a deux!"
Follicly challenged is merely the etymologically correct spelling of follically challenged, which is a euphemistic term for bald men. The use of the word serves to lampoon the perceived overabundance of "politically correct" synonyms for various minority groups, which first emerged and spread in the mid to late '90s.
My father is severely follicly challenged, but he's learned to cope without resorting to a toupee or a combover.