I've found a website called 'Bikini Science'. which is primarily about women's swimwear fashion throughout the ages, but some parts of it include men.
Here is a photo from Italy in 1975:
http://www.bikiniscience.com/chronol.../RS750194F.JPG
There are 3 women at the beach wearing bikinis, but they accompanied by 2 men also wearing very brief costumes.
It's hard to imagine a scene like that nowadays; but I bet back then it wasn't even an issue.