I saw some bloke do this at Liverpool St tube station a few Weeks back - Friday night rush hour (on my way to the Brighton game) My nipper was just saying it would be fun to slide down when the bloke in front of us did just that - don't think he realised how east he would be going when he hit the sign at the bottom - his head over heals dismount was even more graceful that that bloke on the clip - funniest thing I'd seen in a long time. He ran off to avoid embarrassment but had nowhere to go apart from the platform (where everyone was laughing at him)