As always, it depends. Some deer don't care at all. Some care a whole lot.
If a deer has been shot at by a guy that smells like coffee pee, and you pee from your stand after drinking half a pot, I bet that deer will care a lot. If a deer lives on a farm where lots of workers are peeing in the woods all the time and not shooting at him, then he probably won't care much.
Deer aren't necessarily smart but they sure do remember well.
I don't take killing deer so seriously as to worry about it anymore but when I did, I sure didn't take the chance. Plus it's fun to pee from a stand. Especially when there's snow on the ground