I've laughed about this off and on since it came out - not sure of the specific meaning of "wearing concrete underpants" either, but somehow I intuitively "get it" and it makes me laugh!
I agree about the hair, it looks like she's giving everyone the finger. I like the right brain left brain theory, too but I think there is a more simpler translation - "you may as well stop kissing my ass because i'm not receptive".
I think Carol's hair looks like the silhouette of a hand in the "bird" position. Try holding your hand in the appropriate position near Carol's head and I think you'll agree ... of course you might feel silly for flipping yourself off, but hey ... that's the price of progress.