“‘I welcome the opportunity to uphold our finest Wizarding traditions and values—’ Like committing murder and cutting off people’s ears, I suppose! Snape, headmaster! Snape in Dumbledore’s study—Merlin’s pants!”
-- Hermione Granger (DH12)
An exclaimation by Hermione Granger at Grimmauld Place when she realized that the portrait of Phineas Nigellus might report their conversations back to Headmaster Snape at Hogwarts (DH12).
For Americans: In British English, "pants" means "underpants", not "trousers".