It is easy to relax one's vigilance when thorough scans of the 180 to 270 degrees available to forward vision is clear of enemy drivers. With a sigh one can slump a bit, exhale gently and appreciate the security offered by the moment.
And then a reassuring glance up to the center rear view mirror can destroy all sense of security. One of the said enemies seemingly 5 feet back can create a sense of mortality as one feels attacked, violated, and
disrespected.
At one time in my younger years I tried to figure out a way to mount a can of spray paint I could trigger from the driver's seat. I guessed that ruining a paint job was an appropriate consequence, and if they were truly an adequate distance the paint would have dispersed. Never could figure out how to do it though.
On my van, though, I have backup lights switched from the dashboard which will discourage the most aggressive tailgater. They are illegal as they are not connected to the transmission but no one has objected. :-)