> a "popular theory" is just a theory -- just like mine. :)

Rubbish. It's atttested by a string of evidence - it derives from British student life at three or four univesities at around the same time (based on evidence from people like the OED man Quinion quotes) and was widely popularised by Simon Mayo on national radio, from whence it got picked up by all the kids and used in a major national charity event. It's clearly a UK usage since pants means something entirely different in the States and does not have negative connotations.