At the 1965 World's Fair in NY. A vendor at one of the European exhibits wore a black see thru top, no bra. Unfortunately the pockets on the front were multi layer, so no nipples visible.
DR

Not necessarily the first I saw but definitely the first I remember vividly.

I had been working with a girl who would become my wife. We were very good work friends and we were definitely progressing towards the next step.

She invited me to a New Year’s party she was throwing with her friends. I knew the guy she was dating was going to be there but I said fuck it and went.

She has 34dds, that night she was wearing a completely sheer low v neck with a lace bra. She looked like an ad for High end escorts, her cleavage and hard nipples were completely on display. I don’t think anyone looked her in the eyes all night.

After we started dating she confessed she wore that to get my attention since she knew what my likes and kinks were.

Wide Hairy Triangle
 

Not a sheer shirt story, but I did see a very sheer swimsuit growing up. Not sure exactly how old I was, but I was at our apartment swimming pool and there was maybe one or two other people there at the time. A girl at the pool was wearing a one-piece, white swimsuit. When she emerged from the water I got one hell of a sight. The swimsuit was very sheer and I could clearly see her nipples and a wide, triangle-shaped, hairy bush through the swimsuit.

She acted like it was nothing and was completely nonchalant about her tits and pubic hair on display for me and the handful of others there. She kept getting out of the pool and jumping back in, so I was able to get a good eyeful of her nipples and bush. This was the 80s, so naturally, her pubic bush was nice and full.

To this day, I’m crazy about see though lingerie, swimsuits, etc., especially if the girl has a hairy bush.