Near The Knuckle Meaning

(Britain, idiomatic) Risqué, sexual, suggestive of impropriety.

Example: 1972, Nikolái Vasílievich Gógol, Diary of a Madman and Other Stories
  So near the knuckle, I wonder they got past the censor.
2006, Steve Moore, V for Vendetta
  â€œBut . . . Laser Lass is just . . . banging!”
  Stifling a giggle and deciding this must be some masculine epithet she hadn't come across before, Evey gave the handcart a .shove and went on her way. After all, "banging" wasn't anything that was shown on TV these days, even if some of Gordon Deitrich's shows did get pretty near the knuckle sometimes.
2005, Hilary Mantel, Beyond Black
  It's raw, this kind of work, and near the knuckle: unsupported by music, lighting, video screen, it's just you and them, you and them and the dead, [...]