I've always countered that with the following :

Yes, Nazi's, the very trustworthy group that would not lie about calling themselves socialists for propoganda and popularity reasons (post ww1 German public had popular sentiment with socialist ideas). The same ones that went out of their way to then kill Jews, communists, socialists, and other individuals that believed in socialistic ideals.

I'm also sure that the democratic peoples republic of Korea has very fair and free democratic elections!

If they continue arguing about it after that then I know they're a lost cause