An amalgamation of the two words "shit" an "lid". Used to describe a head of hair, or lid, of epicly disgusting proportions. Most probably a badly dyed blond hair cut like the hairdresser was a one-armed chimpanzee with no depth perception.
Usually found heard by 1st XV players dicking on the new guy who needs a word limit so he can't talk during training.
"mate, that is one bad shid"
"a shit lid"