Checking pox - spontanous outburst of pimples occurring when a student notices with 1 minute to go that they've misread the question
Compound fracture - inability to hold 2 parts of a word together. Most common in teenagers.
Consonantipation - usually due to a blockage in the vowels
Tense future - usually afflicts children the week before SATS tests
Homophonia - fear of words which sound the same. There is a related strain occurring in foreign languages, which is an irrational fear of two nouns of the same gender occurring too close to each other in a sentence.
Severe inflection: this could take the form of Phonemonia, or Pluralisy, which usually affects several parts of the body at once
Past tense - Ofsted was last week
Possessive Compulsive Disorder - someone who finds it difficult to share a pencil during an exam.
Punctuated ulcer - in extreme cases, the patient ends up in a comma.
Many of these seem to be mutations of previously harmless bits of grammar. Kept in isolation, or small groups, grammar is benign, but large swarms of grammatical terms seem to exhibit different behaviour, and have a toxic effect on those using them. The misplaced apostrophe has always been capable, on it's own, of exciting high levels of stress and rage, but this is the first time we have seen such dramatic effects in other sections of the English language.