My favorite part of the standard is:
"Deliberate and wary with strangers, he will exhibit curiosity but, most importantly, fearless courage if threatened. However, he responds promptly to friendly overtures honestly rendered. "
To me, that sums up true boxer temperament.
Those who are interested can check out the American Temperament Test Society's webpage and perhaps arrange
to take the test when it's conducted in your area.
Dogs are put through a series of stresses from mild (greeting a neutral stranger, then a friendly stranger, up to a threatening stranger.) In between they're asked to waslk on several unusual
surfaces (plastic, metal), respond to sounds like gunshots and
rocks in a bucket, respond to an umbrella opening, etc.
The test is the same for all breeds, but the expectations for "proper" behavior vary. Gun dogs, for example, are
permitted to look in the air at the sound of the gunshot, while boxers are expected to turn toward the origin of the shot. You wouldn't want a golden retriever to respond to a threatening stranger in the same fashion as a doberman or a boxer.
The threatening stranger starts off as just a peculiar stranger -- dressed funny, muttering to himself at a distance. He never gets truly close, but the judges mark the dog's reactions as it first notices the person up to the point that the stranger "approaches" whacking a stick around and shouting menacingly. A boxer should definitely be signalling with body language and barks that the stranger should come no closer.
The best reaction I saw on the day I went was a little French Bulldog who put all the big dogs to shame with his display of courage. It was a riot!
At any rate, it's an interesting controlled experiment to look into if you are curious about what your dog "might" do.