I tend to ride solo because I stop to look at flowers, and streams, and birds...
The passing bug is mysterious. I was riding up a small mountain one day when another rider came in beside me. "I've been trying to catch you for the last mile," he said. I asked "Why is it so important to catch me?" He had no answer.
When I commuted down the beach, I regularly picked up drafters because I punch a good-sized hole in the wind. They didn't annoy me. The ones who did annoy me were those who would draft, then pass, and then poop out. I'd pass them, they'd get upset, work up enough steam to pass again... and then die again. I never did figure that out.