Every dog is a lion at home.
Henry George Bohn, John Ray (1860). “A Hand-book of Proverbs: Comprising an Entire Republication of Ray's Collection of English Proverbs, with His Additions from Foreign Languages : and an Alphabetical Index, in which are Introduced Large Additions, as Well of Proverbs as of Sayings, Sentences, Maxims, and Phrases”, p.349