The closer to the ground, hence lower, of the two anatomical features whose resident organs govern a man's
decision-making; his crotch.
By metaphorical extension, a man's head is his upper house of parliament, which in some cases vetoes the
ill-conceived impulses of the lower house but is can be overruled by a super majority in the lower house declaring a state of "gots-to-have-it".
A: You see that
disaster Bob went home with?
B:
Yuuup, he definitely let his lower house of parliament
decide that one.
