Angel Station on Boxing day 2007 after graffiti gangs got in over Christmas. What a mess. They had to close Old Street Station (the next stop along) due to obscene racist graffiti allegedly by the same gang. See Mikes blog post about it here:

http://chefdude.wordpress.com/2007/12/27/christmas-graffiti-gangs-strike-at-angel-station-islington/