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I've heard way too many peope unironically quote the show in the real life to believe it's the case for the majority of the audience.
That's probably true, but it's always difficult to say how a line will be used out of context. I guess there are people who used that line whenever they were anywhere near a German, but for them it might well have just been a stand-in for actually goose-stepping around with a finger under their nose i.e., they were wankers.
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It's interesting, there are a lot of comedies like this. A portion of the audience are either laughing at, or with the protagonist and both sets can equally enjoy it. For example, The Office: when Brent creates awkward situations some are laughing at him in pity. Some are honestly laughing with him and how he offends others. Curb Your Enthusiasm, Alan Partridge, Blackadder etc.
They really don't. The joke is that bringing up the war would be insensitive to Germans (and a really stupid thing to say to German guests if they're in your hotel). The line is "don't mention the war", which he repeatedly says to his staff while inadvertently referring to it himself (because he's concussed having been hit on the head by a moose). Of course it's a dig at him, the Germans are just guests who he's managing to offend, just like he offends so many other guests. It's a joke entirely at his expense.