Here's one plausible explanation for fearing and loathing the common pigeon, generously furnished by Brian Q.:
I thought I had the perfect place. Newly rehabbed. A beautiful attic apartment. Gleaming white, with plenty of room, natural light and treetop views at a bargain price. Everything was a dream...until the day I noticed a little "dirt" on my white blender. I thought it was odd, as I kept a clean kitchen, but I didn't pay it much mind, wiping it down, going on my merry way. Later in the day, however, I noticed it was dirty again. But I hadn't touched it. How could it be dirty again? It was then that I crouched down to get a closer look. It wasn't dirt, I discovered. To my horror, it was thousands of near-microscopic insects, crawling and covering my kitchen appliance. As if that wasn't bad enough, I then remembered that my skin had been itching on and off for a few weeks. I thought it was just sensitive, dry skin, but when I took a super-close look at my arm, I realized it too was covered in bugs, buried throughout my arm hair.
Freaking out, I examined my bed sheets. They looked white, but when I looked closer, it was clear, the bugs were everywhere! I wiped my floor with a damp white paper towel. It came up brown with thousands of slimy smashed bugs. They were so small, I hadn't noticed them, but suddenly realized there were millions of them, covering every surface. Trying to figure out how they got on my kitchen counter, I banged the can light fixture in my ceiling with a broom, and they came raining down! They had infested the place, even inside the ceiling and walls. I ran for the shower, scrubbed down, shook some clothes out, got dressed and ran for the hills.
When I came back later to meet an exterminator, he informed me I had pigeon mites, parasites that breed on and around pigeons...of which we had quite a few just outside my windows. He bombed the place, and I packed my bags. Fortunately, my lease was just about up. I escaped without serous harm, except for some horrible nightmares about pigeons, that still haunt me years later.