I hit a few. The nastiest was a few years back in Slovakia, when I had to clean blood and feathers from my helmet vents. The most dangerous was last year when some bird unexpectedly hit my left elbow and I almost rode off the road.
Still, the worst was in my first year of riding, also in Slovakia, got bird poop all over my visor. I was in a village, stopped on the roadside to clean myself, while the local population gathered round to make fun of me. Nowadays I'd just laugh at them, but then it felt awful.