I went out with this girl in high school and through most of college. I should say, first, I had terribly low self-esteem. And she put out. That was about the extent of the reason I was in this relationship, because I was socially inept and she liked sucking dick.
Anyway, whatever analogy you want to use, "dumber than a box of rocks," "IQ of a fencepost," "dumber than a box of rocks that just lost a spelling bee to a fencepost," whatever... it fits.
I finally knew that I *had* to break up with her when she asked me for help reading a tape measure. She was having difficulty with the concepts of half-inches, and half-of-a-half-inch is a quarter-inch, and she was going to start a job doing quality control at a factory.
I got that damn girl through college. I helped her study, I helped her with papers, I deserve my damn name on her degree more than she does. And I knew, as she held that tape measure with a helpless look in her eyes, I just knew at that moment that I would rather kill myself than spend any more time with her.
Not before one last pity-****, though.