And I think you are underestimating how much of a deeply ingrained taboo the nazi salute is for the typical German. You are right, some people can be very stupid, especially drunk. But no German who has not been in some way socilized among nazis would be stupid enough to ever casually do a nazi salute. You just don't do it.
The only exception I might allow besides actual nazis are very stupid or drunk (or both) teenagers trying too hard to be edgy. And even then most people would find it hard to believe that they're not at least right leaning.