Right now, when he's saying things like that, I just COMPLETELY ignore him. I act like I don't hear a word he's saying. And if the kid wants to play with a doll, I'll give him a doll.
He's a good guy and a good dad. I'm not implying that he doesn't love his kids more than life. But it's hard to watch this and I don't want the kids growing-up feeling so pressured to make their dad happy.
I just don't see how this is a big deal AT ALL. Big deal, the kid likes pink and girl's toys. He might outgrow it. He might now. Who cares?
It is very hard to watch when things like this happen, but honestly, there isn't much you can do about it. Even if you say something to the father/mother, chances are they aren't going to change how they are and how they raise their kids. You (general you) can't try and save every child from a parent that treats them poorly, or doesn't allow them to be themselves, etc.
It's not a big deal to you, but it appears to be a big deal to this father. You're right, the kid could stop playing with dolls and could hate the color pink...whatever. But this is a big deal to the kids dad. And being the dad means, unfortunately, that he can raise his kids this way.