Originally Posted by
PlanoFuji
Consider an alternative hypothesis; That the vast majority of people are self-centered a%^hol&^ and react with annoyance (at best) when some creature causes them any inconvenience...
The beauty of this hypothesis is that it doesn't restrict itself to just one class, ie' motorists... Indeed it can easily be seen to apply to other classes, such as cyclists. Just read this thread concerning filtering, or others concerning reasons for Idaho stops, riding on MUPS and dealing with pedestrians, etc...
Refer back to the OP. Motorists got upset when a cyclist held them up by traveling at 15 mph. On the same road, motorists were not visibly upset when another motorist held them up by traveling at 15 mph. Your hypothesis has been disproven, at least in the realm of motorist behavior towards cyclists. The OP's experiment does lend support to the notion that motorists are tribal animals who see cyclists as some reviled "other".