I tried to address this above. I believe the theory is that Patsy was so worked up that she slipped that (and a bunch of other) cutesy crap in there without really thinking it all the way through. Or perhaps not.
Unlike some, my personal "theory" is that John was not there while Patsy wrote the note. I believe he was downstairs dressing JB - thus explaining both the wrong sized undies and the absolutely crazy note. In other words, I think they were both doing a job that the other would have done better. Had Patsy dressed JB the clothes would have been correct; had John written the note it would have been short and businesslike.
I can get my head around that!