I'm queer and basically a gender abolitionist so I am not disagreeing about the social nature of gender, but I think phrases like that are pretty reductive and depending on the context in which you hear it. You can think of just as many supporting examples as contradicting ones. Though, in my opinion we really don't need to "show" that gender is a social construct, for many reasons, but mostly because so many people don't care, and they think social constructs are good, actually.