A large sweatshirt, nothing else

You think of a few different options. All of them have their benefits. Then, an idea strikes you. One of the most difficult things to flash where you used to live was your pussy. Tit flashes were easy. Just wear a low-cut enough shirt or a top that likes to ride up. Or a white t-shirt in the rain with no bra on. Even butt flashes were doable. Just wear pants that are slightly loose with no underwear. Granted, it's not your whole butt, but you can get a surprising amount of it out of the pants without having to worry about the law. The pussy, though? Yeah, that requires staging accidents and making sure they are plausible enough that someone doesn't call the cops. Here, you no longer have to worry about that so you can make up for lost time for both your ass and pussy.

You figure out the perfect outfit for this: your large sweatshirt. You often hang out in it when you wanna be comfy and you can't believe you haven't tried wearing only the sweatshirt before. The biggest advantage to this choice is that the bottom of the sweatshirt comes just under your butt. Any time you move your arms up at all, you'll be giving everyone a flash of your ass, beaver, or both.

You put it on and it feels even comfier than you imagined against your naked body. Oh, you're wearing this sweatshirt like this every single time you get a chance. You solemnly vow to never wearing anything under it again. Alright, time to go!