"It was as big as my head!"
I came across this study in the journal of anxiety disorders. It shows that when we come close to scary stuff, such as spiders or your boss, we think they are bigger than what they really are. People with a fear of spiders taking part in the study were shown some live spiders. When later they were asked to guess the size of the spiders most thought they were much bigger than they really were.
The take-home message is: since some people seem to think that size does matter just make sure you scare them a little before they get a chance to measure!