I was browsing the medieval history threads here and it reminded me of a strange fact my high school English teacher told us. We were reading Sir Gawain and the Green Knight and getting a little bit of background knowledge, and she told us that one of the main jobs of a squire was cleaning a knight's armor of human waste. Since hearing that, whenever I see or read about squires I recall this statement.
I assume she meant after a lengthy battle, which did not permit such activities, but I don't know... What was the idea there? How did they use the bathroom on the road? In battle? Was my teacher full of shit (heh), or did squires really do this?
I am not able to track down old threads, being on mobile... But!
It has been stated here before:
-Soldiers with highly restrictive armor would rarely wear it during lengthy travel.
-Adrenaline experienced in battle suppresses bodily functions.
-Many soldiers did not have butt plates, instead opting for armored skirts which can be lifted or moved about.
-Most full-plate armor was very well crafted and allowed one to drop trou with at most, a few minutes labor.
Personally, I find the most difficult thing to do in armor is to sit in a chair. Breastplates and brigandine are awfully stiff, and gut protection is pretty important. You wouldn't want an unprotected spot there, even in the name of greater flexibility.
Any activity where you simply lean forward is a bit of a challenge. Squatting though, is not impossible.
Tangential to your question, you mention Sir Gawain and the Green Knight. That was written in the 14th century. Plate armor didn't really begin to be worn in Europe until the 13th century, and didn't become all that complex until the 15th century.
The text is in reference to a character who, if he existed as a knight of king Arthur, would've been around the 5th century. It is believed that warriors of that time and region would have warn almost no armor beyond a shield. Obviously, the story is considered a work of fiction and is not required in any way to be historically realistic.