As a guy turned girl:
It’s so strange going out in a bathing suit your first time as a girl. All that’s covering you between your legs is this narrow strip of cloth. You feel naked; it doesn’t seem like enough. But of course, with no penis and balls there anymore, it is. That’s really all you need. There’s still that subconscious fear that your manhood’s going to spill out, even there’s nothing there anymore to spill out.
The second weirdest thing is how there’s nothing down there to be insecure about. As a guy, those baggy swimming trunks do two things: number one, all those floppy bits wouldn’t comfortably fit into anything tight anyway, and second, if you have a small penis, you don’t have to broadcast that to everybody. Your sex is hidden. But as a girl, there’s nothing down there to be ashamed about. There’s no big or small or anything; you don’t have to hide because all girls are the same down there.
And that leads to the third weird thing, which is just how tight it is. It leaves literally nothing to the imagination; everyone can see that you don’t have a penis or balls. Your sex out there for everyone to see, so clearly that it feels like you’re naked. You might as well be, the way it hugs every curve of your crotch, even more if you just got out of the water and it’s sticking to your crotch. Thankfully though, skintight bottoms for girls is something our society has deemed publicly acceptable…. because it makes you feel fucking sexy. Even the first time, you notice it from the get go.
Once you get used to it, that’s when the real fun starts. You catch guys glancing at your crotch and you know exactly what they’re thinking, especially since you used to be a guy. “Holy crap I can see everything! It’s so tight I can see she doesn’t have a penis or balls, but I can’t stare… I hope I don’t pop a boner in my swim trunks…” The best is when you’re talking to a guy and you can just see him absolutely straining not to look at your crotch. That’s when you can have some fun teasing him; spread your legs apart a little bit, tilt your hips forward to show off that gap between your legs, deliberately look away for a moment to give him a chance to peek, pull up on your bathing suit to make it hug your crotch real tight. You know you’ve won when you see him adjust his swim trunks to accommodate his rising boner; bonus points if you can see it tenting his trunks. You don’t even have to be attracted to guys to enjoy it; just knowing that you can have that kind of influence and power over someone is intoxicating.