When you ride the tube (The Underground) by standing in the aisle and and balancing without holding on for the purpose of fun and laughs and enhancing your skills.
Ai! It was a brilliant ride (Tube surfing) today! I picked up at Hammersmith and for an extra challenge rode eyes closed listening to The Futureheads on my iPod.
to balance (hands-free) while riding the subway in London, which is called the tube (hence, tube surfing)
"Right mate, we were kicked off the bloody tube for tube surfing"