Staring dogs are the bane of my existence. Or, well, my dog's.
Well, that and the odd person who walks within about 6" of where I'm crated and then, when the dog goes off, tries to 'help' by standing there and continuing to coo and talk at them instead of *moving on*.
This is never competitors (well, that once, but I haven't seen that person in years, and he really was never nice, just-), but I'm about to start setting X-pens up around my entire area just to keep people out of my dogs' faces. Two of three don't care much, but that third one ends up agitated, worked up, tense, and then I get to go take her in the ring. Works fantastically, let me tell you.