First I would like to thank the voters, readers, and those who gave feedback and left comments. One person gave me a great idea for a future adventure that I can't wait to make happen/write about, and all gave encouragement, so thank you.
For those just signing on, the first part describes my wife's accidental exposure to a stranger, which left me with the realization that her exposure turns me on, and with an increasing desire to expose her again.
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Since the first encounter was an accident, and since I didn't know exactly how my wife felt about it, I started off small. Several times over the course of a few months I would get her aroused while we waited for a pizza delivery, making sure her bra was off and her nipples were hard, and then I would make her get the door when the bell rang. It wasn't quite as satisfying as when she answered the door in a wet white t-shirt, but I was still aroused by it, and it was a start. I think she started getting the idea, because she got in the habit of teasing me when she came back in.
"Look how much of me is showing through this shirt," she would say to me in a playful and shy manner, "my nipples are so hard, the guy couldn't take his eyes off my chest." She would hold her chest in front of my eyes so I would be able to see how tight her nipples pressed against the thin fabric. She would slide her hand up my thigh and feel how hard my sex was, and I think she knew why.
After doing this a few times, and having great sex afterward, I tried to egg her on to show more.