Since our package is located outside of our bodies. If we had our legs closed it would be very painful. And since we are always on the go, we like to feel a little breeze in our junk so some guys what more breeze than others. Now your professor is either horny or drunk or both.
It's uncomfertable to sit with them crossed, to do that we need to readjust ourselves before we can even attempt that or its REALLY uncomfertable, its just not a natural position unless squishing your own balls is you're thing...
Warning: Long answer ahead (tl;dr I'd be surprised if it wasn't biological) I always see answers that point to "scrotum-squashing" or "asserting dominance as the alpha male", but I think anatomy is a more relevant source. I don't experience pain when I push my legs together, and I think pointing to subconscious conditioning is too hasty. What I did feel was my leg muscles getting too tired to justify sitting that way.
There are so many differences between male and female pelvises that it's hard to believe there is no biological differences in hip adduction (force needed to push your legs together). I found it surprisingly difficult to find scientific information on this (it might have been easier if I studied medicine and knew exactly what scientists were talking about). Looking at diagrams, I think it could be some leverage issue with the male pelvis tapering more at the leg joints so the tendons pull the legs apart. It could also just be weaker or smaller adduction muscles in men just due to different geometry, i. e. it's easier for women to pull their legs together. Like all things in science, it's probably way more complicated than I think it is. If it is biological, it could be justified by the scrotum-cooling idea. Scottish men who wear kilts are known to have higher-than-average fertility rates, probably because their testes don't overheat. So differences could be sustained by sexual selection.
Lol are you shy? Are you uneasy knowing he's letting his wang get some breathing room right in front of you even if it's concealed by clothing? I think we do it, because we honestly don't give a crap lol.
I think the point is really girl sitting with legs wide shut closed because of the societal standards about sex. I think the natural way is sitting with legs open. I've just recently met a girl who does that and I was like "f*** what?" because to me it was like an invitation to dive into her p****. But see pics of gorillas in the wild, look how they keep their legs open, and their postures in general, just like humans'. it is indeed true that the posture may sometimes be accentuated, and that's to put the d*** in the limelight, inviting for sex, or telling you they want to shag. I've done it myself
I sit with my legs wide open. lol. That's why I don't wear dresses or skirts, well that among other reasons. It's comfortable, feels natural etc. But I also do it as a little rebelling thing towards my dad. He made me attend these f***ing etiquette classes when I was a kid, and one of the things we covered was how to sit properly. Because I'm a "lady", I have to sit properly and primly like I have a f***ing steel rod rammed up my ass and spine.
The reason why guys do it though is pretty obvious. They have a penis and testicles between their legs. Also, it is scientifically proven that the wider a males legs are apart, the more dominant his personality and the larger his penis. Because I sit with my legs wide open my friends always crack a joke that I have a one-hundred foot long penis. Impressive, eh?