It's been acceptable as long as there have been real guys confident enough to rock it.
Regardless of the style, in fashion or not, I've forever failed to see how you can stick the "gay" label on anyone just because of what they're wearing.
If anything, the fact that people questioning this or any other style of running gear and spend time worrying about what someone else is wearing says a lot about your/their own self confidence.
I've never been afraid to wear what I feel like wearing at the moment, whether that's still the 80's styles, short short spandex, more colorful gear, whatever. Call me what you want, I get more compliments from women than I could ever count because I'm not one of the sheep that has to follow the latest trends and spends time worrying what others might think, like so many of your mindset.