Well, there is a 90 percent chance this is just a phase, and he'll grow up with a secure boy identity. Assuming that happens, it will do him no harm to go through a brief "pink" phase. It will just help him to value and respect the women in his life.
And then, there's a 10 percent chance he'll grow up to be gay, and/or that he'll have a nonconforming gender identity.
And guess, what. You have no control over this, either way. It's a roll of the genetic dice; it has nothing to do with whether he's allowed to express himself or whether his self-expression is repressed. What you CAN control is how loving and accepting a parent you are.
If you love and accept him no matter what, he will (most likely) grow up to be a straight man who loves and accepts women and who treats LGBT people (and everyone who's different in any way) with respect. Or, he'll be a gay man who accepts and respects himself and is a role model to everyone around him.
If you choose NOT to be a loving and accepting parent, then, well, none of these good things will come to pass. I'm not going to go into the various doomsday scenarios, but they are ... bad.
In terms of teasing, the kids who need to change are the kids who are teasing, not your son. Please don't teach him to be intimidated to the point of hiding who he is. Teach him to stand up for himself, loud and clear. Sign him up for karate. And, just as important, teach him to use humor and get the bullies on his side.
My own son went through a phase at 5 where everything had to be pink. So, we got him a pink scooter and a pink booster seat. Now, at 7, he has a very secure boy identity -- and he's a confident kid. He's not really a sports kid, but he's all about Ninjago and Harry Potter. I really think that respecting his play choices helped build that confidence.