A man sits in a car guy sipping a cold drink, then puts it between his legs. Another fellow gets into the passenger seat and puts an even bigger cup of soda between his legs! The first guy eyes the other guy's lap, then looks down at his own smaller cup -- an obvious play on penis envy.
While the ad doesn't actually deal with homosexuality, it does deal with the related area of men's examination of each other's "genitals" and bears examination. This could easily have also been handled with a negative homophobic reaction but was not.