If you ever do feel like arguing with them, any time someone brings up the "Social Construct" argument for anything, remember, a social construct requires a social contract. If it isn't objective, it requires me to agree with you in order for your definition to make sense. So if I don't agree, you by extension have no position, therefore I'm right, as the only position left in the argument is one that does not require agreement with onlookers, it is objective, not subjective.

And then just hammer on the fact that you can't use subjectivity on an objective measure unless all sides agree with the subjective measure, which you don't. They can't find flaw with the objective measure, because for most intents and purposes, it is objectively true.