My 2 girls were having their nails painted when my ds asked for his to be done too. (dds are 5 and 2, ds is 2, twins). Of course I did it, he loved it, looked fantastic......DP was not amused, and kept saying to ds, its not for boys, its a girls thing blah, blah, blah. I was quite surprised because DP is usually relaxed about this type of stuff.
Anyway, I think it is completely fine and why on earth should anyone deny a child this if the others are doing it? Its no different to dressing up. I explained to my DP that if ds still enjoyed having his nails done when he was say 6, then it would be up to him to decide how he felt, particularly as then he will notice that most other boys don't have their nails done.
Its fun, its normal, its harmless. I'm sure it does not make little boys grow up to be gay men. AND if my ds does grown up to be gay I couldn't care less, he is adorable with or without the painted nails and always will be for me.
I'm not ranting at anyone here, I've been keeping that in since DP passed comment