One point is that being in an actual war changes the rules. If you're caught in a desperate fight for your civilization, you'll put civility on hold, because being polite wouldn't do any good and you're too busy being desperate. But unless you love living like you're in a warzone, you probably prefer to maintain civility at all other times.
So you ask what one should do in 1934, on the cusp of war, in a pre-war situation. That kind of depends on knowing that it's a pre-war situation and knowing that things are desperate and that you should throw civility out of the window. If I was strongly aware of that fact (as some were), I'd be thinking mainly "how do I keep a low profile and escape from Germany," not "how do I tell the fascists that I disapprove of all they stand for".
But I suppose there's a kind of antsy ambiguous semi-desperate state that just makes people angry without fully committing to desperation.
Post-war is different of course because then you've won, and it's socially acceptable to be rude to nazis, the conventionally accepted bad guys. Common consent encourages it. It's a civil kind of rudeness!