Not unintentional but enjoyable. When I was in high school, a boy did it to his hot girlfriend (yes she was 18) at a friend's pool party. I still remember the brief glimpse of her tits.

I am completely in the same situation. Although there are a few of our male friends who have seen my wife's boobs, mainly from being on holiday with her before we were together, I've never had the fortune to see any of our female friends tits. We have been on holiday with a few other couples but there was never any topless sunbathing on those occasions; not even from my wife. This is a massive shame as seeing close female friends, friends wives, girlfriends, and femal in laws topless is right up there top if my list.

I have seen my neighbour's boobs one hot night; too hot for her to be wearing anything to cover her breasts. This wouldn't normally be a woman I'd look twice at in the street, but the fact I'd talked to her outside her house that morning, and there she was topless standing at her window, was so so hot.

Because my wife and I attend lots of biker type events, we see LOTS of topless and nude women all the time. After a while you can actually become a bit desensitized to it. BUT, it's always a thrill catching a glimpse of someone you actually know! I'll never get tired of that!

For me also breasts of women I know.
It's always a bit more special (not necessarily in a sexual way) than seeing a stranger's breasts.
Unfortunately, such occasions do not occur that often.
When visiting nude beaches, nude swims or sauna, it are usually strangers we see.

Some situations when I did see familiar women' s breasts are:
- My SIL (wife's sister): she joins us sometimes when we go to nude swims or at the sauna center. She's got nice DD's although they sag a bit after 2 kids.

- 3 female colleagues of my wife. We met them at the sauna center one day. Quit funny to bump into each other like that stark naked.

- girlfriend of my best friend and her female friend. They were about 19 at the time. We were all in college and had rented a cabin with some friends. Her friend and I were single and we shared a room with them. It was summer and very warm. So when we went to sleep, friend and his girl came naked out of the bathroom indicating it was too hot to wear anything while sleeping. Her friend decided to only wear a string and I also went naked. It was the 1st time I enjoyed social nudity while chatting with them for some time. Luckily, I was in the right bedroom, cause the ones in the other room (2 couples) wear complaining at breakfast it was so warm sleeping in their pj's.

- A friend of ours who just gave birth. We went to visit them in the hospital. At a certain moment, she needed to pump away milk cause she was producing too much milk. So we suggested to wait outside, but she insisted that we stayed. My wife helped out a bit (she's a pediatric nurse), but I was just sitting there looking at a pair of DD's of which the nipples were moving up and down.

- A friend of mine who had smaller breasts (A or small B cup). She often did not wear a bra cause her breasts were still firm and perky. That resulted in an occasional downblouse presenting a nice but bit obscured view. However, one hot summer day, she woar a pretty open blouse with spaghetti straps. When she bended down, I got an unobstructed view of her breasts and nipples. She really had a nice pair with smaller areolas. So being a gentleman, I motioned to her to be careful when bending down, cause there wear a lot of people around of which I was sure she didn't want them to see what I just saw. Later that day she thanked me for pointing it out to me and asked me how much exactly was on display. I replied honestly by saying that she had 2 nice birthmarks on her left breast. That made her turn deep red cause she knew those were/are located next to and just below her nipple ... meaning that I saw everything. Her response was that she was glad it was me who saw and not some of the others (who could be jerks about such things). After that time, there were some other downblouse moments, but never again such a full and nice one.

I was about to say something similar. It only takes a few seconds to pull up an endless amount of boobs online so seeing them isn't as much of a big deal. The same with lifestyle events and nude beaches. I don't think anything of it. But, give me the chance to possibly get a quick look down the shirt of a woman who is taking things out of her carriage at the market. I'll jockey for position for that. As for someone I knew vs a stranger... yeah, seeing someone I know is more exciting but then all that goes away after seeing them. I have a female friend who I've known for about 30 years. She's one of the very few female friends I haven't slept with. There have been a few times when I've got a quick down blouse but that's it. She recently showed me photos of her and her boyfriend (LS profile). She was nude and getting it from every direction. The intrigue was gone after seeing them so it really wasn't as hot as it was in my head before she showed me.

Even my wife. She has great tits that I was looking forward to playing with when we first met. And not that I don't appreciate them now but she can be topless and not get my attention as much as she did the first few hundred times we were together.

Boobs I know
 

Boobs I know for sure!!!

The excitement of getting pics of a female friends boobs can't be topped.

We've all looked at the bra shapes on her and extrapolated what might be underneath. We've added data on jiggles, downblouse peaks and hugs. When an in person sighting happens, its great.

My favourite is the unexpected pictures. Especially if its among a friend who is at the top of the list. I have been lucky enough to land pics of my wife's two friends who's tits I would most want. I've been angling quietly on a third friend that I am sure I will eventually get. 10/10 go to spank bank stuff.