What does it mean when a man is called 'gay'?

In a heterosexualised society, to say a man does not have interest in women is to question his being a man. In traditional societies it was not about interest but about performance. If you could produce a baby (the actual sex happened in strict privacy)it was assumed by the society (this was of course deliberately, the society where men's spaces still had a lot of say, wanted to give men that leeway, where their disinterest in women was not visible to anyone since sex happened in absolute privacy and the woman could not talk about what happened within closed walls) that the man can have an erection and can perform. Of course, it was also true, because, eventually it didn't matter if the erection came after a lot of cajoling... that it did get erect was the symbol of 'manhood'. The men of course sacrificed a lot of their freedom and inner self to fit into this tradtional role, but still they had a lot of leeway.
But the heterosexual society leaves men no leeway. You have to show an active interest in girls. And when there is no social barrier between men and women, that interest cannot just be in words. You have to materialise that into action. And it becomes really oppressive for men.

So, when a man is asked if he doesn't have an interest in girls, it means basically to challenge his manhood, his place in the men's space (which is although now heterosexualised). And if the male is masculine gendered he is going to be extremely upset. Of course, men never want to be in a situation where anyone can say that. So they do everything to avoid that. They go through a lot of stress to invent a sexual need for women, even where none exists.

Of course, who would say such a thing. When a friend says this, this is to exert peer-pressure... but when a unfriendly person says that, it is a direct challenge to your manhood... and this can only be said if you are vulnerable, socially week (in the sense that you don't have enough social manhood).