Eh... Depends on your point of view. How much gayer is it to give yourself a handjob? Or to shoot your own load on any other part of your body? Or self prostate stimulation? When it comes to doing things by yourself, I don't think the normal labels of sexuality really apply. If a man enjoys taking it all from another man, then that's a whole other story...
I've done this once -- by accident. And it really isn't a big deal. I was more surprised with how forceful it was rather than the fact that some of it ended up on my face. It's funny how you can surprise yourself sometimes!