This expression indicates a /prog/tard's confusion and lack of understanding. When confronted with something he can not understand or respond to, /prog/tard mumble "Muh SICP" or "Muh back to /g/" This is usually followed by post saging and foot shuffling.
I'd like to share a revelation that I've had during my time here. It came to me when I tried to classify your species and I realized that you're not actually posters. Every poster on this website instinctively develops a natural equilibrium with the surrounding environment but you shitposters do not. You move to an area and you spam and spam until every thread is corrupted and the only way you can survive is to spread to another thread. There is another organism on this website that follows the same pattern. Do you know what it is? A spambot. Shitposters are a disease, a cancer of this site. You're a plague and we are the cure.