You guys are trying WAY too hard to troll this series. Go to /gif/ if you want boobs. Shikamaru's knee gets a panel cuz, stylistically, comics do that sometimes. Take a look around. You'll see random bodyparts getting their own panels, their own sound-effects, all sorts of stuff. Kishimoto's poorly drawn knee isn't the first and won't be the last.
PS: You'd have better luck with the boobs if you remembered Jiraiya's estimation of Tsunade's bust-line when Kakashi 'remembers' what 106 possibly meant.