"You are wearing Van's, how can that be sustainable?" - Easy, by wearing them for quite a long time and not buying new more sustainable shoes as long as they still work.
This or something quite similar probably everybody has experienced that told his or her friends that one wants to go more sustainable in their own life.
I stopped eating meat about one year ago, now I am entirely vegan for like two months and I commited living a neutral and sustainable livestyle wherever I can.
This means, I am doing research before I buy things, before I purchase clothes for example. My criteria is pretty simple: I don't want that anyone has to suffer, so I can wear clothes.
Another rule of thumb; I am only replacing stuff that is broken, that doesn't mean I throw out stuff that is still working. Those Van's for example; it would be pretty unethical to just throw them away, so I can tell I am your vegan next door hipster that is only wearing stuff out of hemp.