Several close calls in this department:
Georgia, late 70's -- I was travelling to the Everglades with my aunt, and a slim, long-tailed bird with large white wing-patches flew across Interstate 75. In what was to become her life-long obsession with mockingbirds, she locked the brakes on my Ford Maverick, reaching for her binoculars, all the while shrieking "Mockingbird! Mockingbird! Mockingbird!" until we came to an abrupt halt after nearly ripping the passenger doors off on a guard rail. Two other vehicles suffered minor dings, and, as luck would have it, the second victim was a Georgia State Trooper. He was angry, and we were driven to the Tifton Courthouse, where I tried to explain things, waving credit cards and U.S. cash ... well, she picked up five tickets, I paid for the vehicular damage two days later, and we resumed our trip in a rental. I drove.
Aurora, Ontario, 1984 -- Reports of a Hawk Owl were circulating back in the days of the Globe and Mail Birds column and word-of-mouth. Off we went in my 1978 Plymouth Fury. It was some unpaved road, and there were quite a few vehicles parked every which-way, tripods all over, and we joined the group. The very agreeable vole-biter was perched on a tv antenna (remember them?), and Margaret, not entirely familiar with the ways of owls, began waving a hot dog and bellowing, "Here, Ollie! Here, Ollie!" to the bemusement of the other observers. One group, who'd driven from Rochester, immediately locked themselves in their vehicle.
Well, A York Regional Police cruiser (talk about bad timing) just happened to appear on the scene, perhaps for a donut-break, and the officer, seeing all the cars and tripods and, I suppose, the hot dog thing, approached, nervously. We explained that we were there to look at a bird, which didn't seem to register immediately, as his attention seemed to be occupied with the hot dog. After a few minutes of silence, we were advised to park our vehicles to the side of the road and not impede traffic (?), before he made a hasty exit from the situation. No tickets this time.
There are more stories, but I must say it's a little less suspicious to be wandering about with binoculars these days. For an interesting tale germane to this topic (and a fascinating historical account of birding in the Toronto area), I refer the reader to Richard M. Saunders' Flashing Wings, published in 1947. Ornithologists armed with optical equipment during WW2 certainly attracted more attention when they found themselves near military bases ...
Cheers.