Penis Preference!
While I agree, penises are totally the best thing ever, but here's the problem: we don't entirely understand vaginas. Please, biology majors: vulvas are a mystery to men because you're not studying them. When one set of genitals gets more attention than the other, like, 5x as much, then the other one feels frustrated and left out and taken advantage of, while the one that got more attention gets to take a nap. Make biology mutual, and give her parts the attention they are due, biologists.