Full cross if you're wearing dress slacks and either a tie or a blazer. It curtails the urge to sit with your legs wide, like you're airing out your crotch. I was sitting in a van in Third Form with a bunch of girls when one of them grabbed my knees and jokingly put them together because I was taking up too much space, nothing else came of it though.
I'm neutral on the subject and couldn't care less how a man sits. But personally, I find it uncomfortable as it feels like I'm crushing my balls. Gotta let the boys breathe.
I fully cross my legs. I never considered half crossed as any more masculine than wearing a beard being more manly than clean shaven, which many societies in the world believe. Then again, I sometimes wear pink ties and a pink sports shirt which perhaps certain people in small towns in Arkansas would frown upon.
The full-cross is, IMO, more appropriate for professional/formal settings as it exudes a bit of sophistication, whereas the partial cross is more appropriate for everywhere else, as it is more overtly masculine and casual. I, for one, cannot for the life of me get my legs to fully cross anyway, so I'm a partial crosser. As someone else said, there is also the cultural aspect to take into consideration. In the Arab world, for example, you need to be careful about the partial cross because exposing the sole of your feet/shoes to someone may be deemed an insult. Interesting that this thread came up, as I recently took a weird interest in the topic myself.
But look at those crossed legs though!!.. lol Great post, sir. Very informative and coincides with many day-to-day situations of EVERYONE who posted. Bullish like this.. Spoiler only exposes the unjustified, over-the-top, pre-mediated hatred against yours truly. Guess what though... Harden's defense still sucks and it's not my fault. Don't blame the messenger.. lol. The VOTE in this thread is 50-50%, tricks.