Lol, it's not actually all that serious for CB power... you dose yourself with way more bad wavez every morning if you use an electric razor while it's plugged in. The main thing is actually losing efficiency… At the frequencies that a CB radio uses, the little tiny metal pole is only part of the antenna. The metal pole and a big flat grounded metal surface below it work together to propagate the signal away from the antenna parallel to the flat metal grounded surface and perpendicular to the long metal pole. The longer the flat metal grounded surface below the antenna stretches in a particular direction, the more power the signal will have in that direction.
In other words, if you mount your antenna pointing straight up on the very left side of your bumper, the signal will be the strongest directly to the right of your car because the flat metal surface (your bumper) stretches the farthest distance away from your antenna in that direction.
There are two problems with mounting an antenna inside of an A pillar:
1) The direction the antenna points is not exactly 90 degrees from the grounded reflecting surface (in this case, the hood of your car – at least in the forward direction)
2) Much more importantly, the antenna in parallel with, and in close proximity to a grounded pole (the A pillar itself) that both acts as a sponge to soak up the signal, and assuming the antenna is mounted between the driver and the metal, reflects a lot of the signal right back into the car where it bounces around and soaks into everything in the car. (Like food in a microwave oven… though MUCH lower power.)
/While I’m at it, there’s something interesting about microwave ovens that a lot of people don’t realize.. They’re tuned to roughly the oscillating frequency of water molecules – that’s why anything with water content gets super hot, and dry things generally are unaffected.
//The more you know...
///I should add that while antennas themselves are not entirely dangerous, higher wattage definitely is. If you were unlucky enough to grab a bare antenna while even a 25 watt signal was being transmitted over it, you would instantly burn your hand badly enough that you might need a trip to the ER. By comparison though, the most power a normal (non-single sideband) CB can legally transmit with is 4 watts.
Now here's a video of a 28,000 watt FM antenna almost instantly setting fire to fire retardant material. 
According to Top Gear, all truckers talk about is murdering prostitutes, so you're not missing out on much.
