1) The area between two opposing forces' trenches during WW1. Characterised by a quagmire of saturated soil, crater holes, barbed wire, unexploded shells, quicksoil and rotting bodies. The last place on Earth you'd want to be in the period between 1914-1918, or for some time afterwards I'd imagine...
2) The area between your ballsack and your arsehole.
"I love scratchin' mi' No Man's Land, *guffaw guffaw.*"
Guy 2:Yeah, I fell sorry for you man. BBW and psycho ex girlfriends never make for good company.