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.
by Turd Bard October 9, 2014
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