"To play square" is to be up front with someone. Honest. Straightforward.
"In all its thudding glory" describes the thudding pain of a headache at its full strength. While the expression "in all its glory", spoken in sincerity, would mean that something is truly splendid; beautiful; glorious, it is most often used ironically to indicate a certain disdain: "The Emperor stood naked before them, in all his glory". His nakedness was anything BUT glorious.
I expect that that is "as clear as mud!"