This term “nao can ti”, meaning literally “brain-impaired writing style,” is the Chinese answer to “l(fā)eetspeak” in English. It’s a language used by some netizens who mix traditional and simplified Chinese characters with symbols, numbers and alphabets. It is so hard to read that it looks like the writing of a mentally impaired person.
This language is quite popular among young netizens who on one hand would like to show their independent personality, on the other hand, want to keep some privacy from their teachers and parents.