The dreams started in hi-skool.
After the florpus incident, and many failed attempts at contacting The Tallest, Zim eventually gave up and decided he was going to take over the earth his own way, without anyone's approval. Zim started watching movies about "hi-skool" to learn how to gain his peer's approval, and it surprisingly worked. Zim started wearing more human fashion, mostly consisting of pinks and purples. He'd often wear skirts with leggings and heels since they were casual but similar enough to his invader uniform. He also found skirts way more comfortable in general.
The first time Zim showed up to skool in a skirt, Dib laughed, but his classmates quickly started praising him for "defying gender roles". Zim never understood why humans assigned fabrics and colors to their version of gender. On Irk, the only things that were considered "gendered" were antennae and eyes. Everyone wore the same clothes that mostly consisted of pinks and purples no matter your gender.
Along with a wardrobe change, Zim also changed his wig to be more "trendy", now with bangs that swept over one eye and a purple dyed streak. Purple was Zim's favorite color and it showed. Ever since he first arrived, his contacts have always been that same shade of blueish violet.
Dib began to take notice of Zim's changes. He grew mature enough to realize that Zim would never succeed at taking over the earth, but he still felt the need to keep a close eye on him. They became sort of frenemies, in a sense. Soon enough, his hormones caught up to his obsession and he starts having dreams. They started shortly after Zim started wearing human clothes. Zim flaunting his new fashion sense must've gotten to Dib's head. He pictured Zim on top of him, taunting him by grinding against him in that damn lavender skirt he seemed to love so much. God, sometimes he just wanted to bend him over and give him what he deserved.
Did Zim even have genitalia? That was another thing. Dib's obsession with Zim's anatomy had turned sexual.
It didn't help that Gaz offered to help Zim with his new interest in fashion, much to Dib's chagrin. Dib never had much of an interest in fashion. He still wore the same black jeans with a t-shirt, only now it was grey with a dark grey alien on it. The same black boots, and the same trenchcoat, only now in a larger size. His hair was starting to grow longer in the back, almost like a mullet, and his cowlick had become longer and jagged. By the time he was 18, he had a small patch of stubble on his chin.
He still had that reputation of being a weird shut-in, and now on top of that, it was clear he didn't shave. Still, there was one girl who's always been drawn to him.
