Married couples are remarkably coy about being naked in front of each other, to the point where even after, as del so delicately phrased it, 'satisfaction' the woman carefully holds the bedsheet up to her shoulders and the man is careful to have the bedsheet so high up his waist that not even the happy trail is visible.
On a related note, whenever a couple kiss for the first time they never bang their teeth together, get a nostril full of the tip of the other person's nose, lock up in panic then pull quickly away because they had the fish in parsley sauce in the restaurant earlier on and now find themselves discretely burping every couple of minutes, or any of the myriad other things which can make first kisses a bit awkward.