No, the National No Pants Subway Ride hasn't become bi-annual and it's not some sort of weird art installation - the nudity on the subway is down to a bet and some kind "friends".
Dennis W, kindly sent me a link to this story which shows how commuters on Prague's Metro are just as blasé as London's Tube travellers.
When the naked man boarded the subway everyone pretended that nothing was wrong:
" 'People were looking everywhere but at him', one of the passengers said later. After a while someone must have alerted the metro staff because the police arrived, covered him up and led him off for questioning.
It emerged that the poor man had lost all his clothes in a bet and his friends had pushed him out of their car in the middle of Prague stark naked. 'He was only trying to get home as fast as possible and he was dreadfully embarrassed - so we let him off the hook' a police spokeswoman said later. "
Lucky that a photographer was on hand to preserve the moment!