I know that it's the person in the rear who would go down, if tires touched, but I figure that it's OK to expect some semblance of manners on the road and a stranger presents unknown dangers. Also, I have enough to do in dealing with those who fancy themselves 'elites' or above silly voice warnings or turn signals and blow past me w/o any notice; then there are the variety of users on the multi-use trails that I've called out to and am trying to negotiate my way around wayward roller bladers, chatting strollers walking 3 across who MOVE LEFT when I call out 'on your left', young children on bikes who ride the entire breadth of the trail, etc...as well as those coming in my direction - lots to think of already, so I am not concerned with waving some selfish and silent wheel sucker off or hurting their feelings. I know of an experienced rider's death from head injuries when an inexperienced rider lost control of their bike and hit him, sending him into an endo and suffering fatal injuries...those things stick with me and I won't apologize to anyone for trying to keep myself safe and alive...