This is a true story: my last GSD went to work with me every day, and in the course of the day he's see about 2 dozen or more people. Some of them even brought treats along - he had it made, lol. Anyways, he would nap when nothing was going on. Every time I said, "Hi" to someone coming into my work area and he was woken up from his nap, he would bark. I think he didn't like the fact that I was the first one to notice them, lol, but hey "you snooze, you lose". So after a time he conditioned himself to bark every time I said the word "hi".
This was a funny joke, and I ended up greeting people with the oddest phrases and in different languages just so I could avoid having him shout "Woof!" and this even happened at home, when I was on the phone. I really had to watch what I said unless I wanted a bark, lol.