It represents sexual pleasure and we don't even realize it. Why, you asked?
Simple. Blue eyes makes the pupil look bigger since it's a black dot (the pupil) on a light color background (blue).
A larger pupil is usually associated with pleasure. Just look at how the pupil reacts when people do drugs.
You can also observe the pupil growing larger when a lady (or man) interested in you looks at you.
EDIT: My weakness? Green-eyed ladies.