Get the pip
Become irritated or annoyed.
It isn't likely that anyone would guess the original meaning of 'the Pip'. The odd fact is that it was coined in the 15th century as the name of a respiratory disease of birds. Specifically a disease that had a typical symptom of a white scaly patch on the tongue. This is first cited in the Middle English translation of the 4th century Roman writer Palladius's
De Re Rustica, circa 1440:
And other while an hen wul ha the pippe,
A whit pilet that wul the tonge enrounde
Contemporary with that usage is a reference to a human disease. This appears in John Lelamour's translation of the 15th century herbal guide the Macer Herbal:
Playnteyn helithe the pipe [Plantain heals the pip]
It's good to find a use for plantain, which most gardeners revile as a noxious weed.
Some early citations concerning the human disease Pip refer to it as a disease of the mouth and it may be that duplicates the bird disease name. Other citations are quite varied in their context and it is more likely that 'Pip' was a jokey disease name, somewhat like 'lurgy' or 'nadgers'.
Most references to 'the pip' related specifically to the bird disease, which appears to have been well known and is frequently referred to in print. People in poor spirits were described as 'like a chicken with the pip' etc.
It wasn't until the 19th century that the specific avian references were dropped and people who were were annoyed or dispirited began to be described simply as having 'got the pip'. An example of that comes in High and Low, a novel by the English author Henry Coke, 1845:
"Yes, will you come?"
"I want to come, but here's More says he won't go."
"What's the matter, has he got the pip?" inquired his lordship.