"You can't tell a lie yet you then immediately lie about wearing it. I know you wouldn't." Sure he doesn't know Skulduggery very well, but judging from the suits, the car, the entire persona - Max can just tell that he wouldn't be caught dea-- er, well, wouldn't wear the shirt.

Or in this case the multiple shirts spliced together by some insane clothing scientist that deserves to be shot.

"Go ahead and wear it then, if you're so attached."

Bluff called.