Erm... I think you forgot your pants!

Why are people around the world taking their pants off? Read on! :-)

Passengers all over the world travelled without their trousers in a cheeky international stunt for 'No Pants Day.'

Organised by US practical joke group Improv Everywhere there was a co-ordinated subway ride across New York City, the Mirror reported.

According to the official Facebook site, people were invited to take part in travelling without their trousers as long as they could keep a straight face.

The craze spread to London with a group of Arsenal fans pictured in their underpants ahead of their game against Manchester City at the Emirates.

The stunt also spread to Stockholm, Sydney and Shanghai as stunned tube, metro and subway users looked on, bemused.

The organisers of the 12th annual bare-legged event gave the thousands of brave participants' detailed instructions to sit in the (subway) car as they normally would and read a magazine or whatever as they normally did.

The organisers told them that their team leader will divide them into smaller groups, assigning their group a specific stop where they will remove their trousers.

As soon as the doors shut at the stop, they should stand up and take their pants off and put them in your backpack, the organisers said.

They said that if the participants liked to use a briefcase, purse, grocery bag, or whatever instead of a backpack that was fine as well.

And if anyone asked asks them why they'd removed their pants they should tell them that they were "getting uncomfortable", they said.

The organisers asserted that the participants should exit the train at their assigned stop and stand on the platform, pantless.

They said that participants should wait on the platform for the next train to arrive and stay in the exact same place on the platform so that they enter the next train in the same car as they exited the last train.