"Feminine" refers not just to literal females but to anything that possesses or is imagined to possess stereotypically female qualities; a man can be feminine or strike a feminine pose. Various cultures attribute "femininity" to obviously genderless features of the natural world, like the moon or the soil (the ancient Chinese identified the ground as feminine with a masculine sky above). There are feminine rhymes in poetry. If an abstract linguistic pattern can be feminine, why not a penis?
A feminine penis is soft, small, and cute. But the thing you notice most is how non-threatening and friendly it is. Every time it rises in greeting because it's happy to see you despite it not even having the vigor to go up the whole way anymore always puts a smile on your face. That earnest joy and pleasure it shows when you're around lets you know the girl really is in to you, too. With how lovable and inviting it is, you'll find that it quickly becomes your best friend in the whole world. For example, a slender, smooth penis, contrasted with a blunt and veiny member. A graceful penis. A receptive penis that does not aggressively penetrate but rather allows itself to be engulfed. And isn't dribbling semen reminiscent of a breast's warm milk? A nurturing penis, a penis like a doting mother.
How can it be gay?