Your next-door neighbor is an exhibitionist and you're a voyeur. There's nothing wrong with that. I'm a bit of both.
When I was just out of college, I used to walk my dog every night. Every once in awhile, as I passed this house on the corner, a young guy about my age would stand in the brightly-lit front room window full-frontal naked. He was nice-looking, with curly dark hair, a decent body and a somewhat small-to-average-ish cock. I never knew whether he was an equal-passerby exhibitionist or whether his show was only for me and my dog.
My wife, prior to our marriage, had a next door neighbor who used to exhibit occasionally for her and her current boyfriend's benefit. One night while I was there, her boyfriend came rushing into the front room, exclaiming, "He's on!" We scurried into their darkened bedroom and took up watch. Across the way in a fully lit bedroom with the curtains wide-open, was a young, fairly hairy, stocky young guy, completely naked, humping his pillow. The buildings were close together, so it wasn't difficult to make out detail, plus things were greatly enhanced by a pair of binoculars. His cock was like the nursery-rhyme teapot: short and stout. After a few minutes of vigorous thrusting, he rolled over and finished off with a frantic hand job. Then he rose, walked to the window and closed the curtains on the evening's entertainment. I wonder how he'd have felt if, during his performance, he'd heard my wife's boyfriend's smug, whispered boasts about his own superior endowments!
I shouldn't appear so virtuous. I've had my bouts of exhibitionism. At the time I was walking my dog, I lived in an apartment where both my bedroom and front room faced a building across the way. Both rooms had full-length sliding glass doors. I seldom closed the drapes. I was fully aware I could be seen when it was dark when naked in my bedroom and while crossing from the bathroom to the bedroom, or occasionally when I'd dart into the front room. It was a kind of rush. I later had confirmation of this. I learned a gay friend once lived in the building across the way. He'd many times enjoyed seeing me au naturel. And, occasionally, his friends. He too had a handy pair of binoculars. He needed them. I'm hung like a chipmunk, and he'd be in serious danger of a squint looking at my junk without them.