Calm, Forward, Straight asked: How does one mess up one's "piloerection"? I'd hate to do it by accident :)
Well, the simple answer is, piloerection is how I make the hairs of my coat stand up away from the skin. Depending on how cold it is, I want more or less air trapped by the hairs next to my flesh. This is how I regulate my temperature.
So, when it is really cold, I look all poofy, because everything is erect. If I am sweaty and hot, all the poof goes away, so I can dissipate body heat and dry off... whence my coat will regain poofiness (precise loft dependent on temperature).
If Mother brushes me when it's really cold, the pressure and static mess up my poofy bubble, and it takes time to get it perfect again. In winter, a lot of times she'll curry me really well, or brush really well, but usually not both.
I hope that answered your question.