When I'm alone and plodding along the shoulder of a state highway, I like to stand up to catch a wind gust as large vehicles "fly" by me. The amount of "fun" I get from this is exponentially proportional to the size of the passing vehicle. Unfortunately, I have a few concerns regarding my mischievous behavior.
Since my average speed is about 15 MPH , I'm typically only in the slipstream of the said vehicles for a short period of time. Does standing up for this short period of time actually give me a substantial increase in speed?
Also, I often wear highly recognizable clothing and/or gear. There may be a few non-cyclist motorists that recognize me. I'm concerned that my act of standing up right before I'm getting passed could be perceived as "aggressive" behavior. If I continue to stand up to maximize my slipstream from passing motorists, do you think I will encourage some motorists to dislike me more than they already probably do?
 - My maximum speed is 40 MPH but that's downhill. Also, I can typically get up to 20 MPH on a flat way when there is a strong tailwind.