Even the crustiest old caretaker, at a word and a smile from Captain Valentine, would allow me to seat myself on the glass cases.
And you know what a fellow old Splinters is, the crustiest of the crusty.
c.1400, from crust (n.) + -y (2). Figurative use, of persons, "short-tempered," is from 1560s.
Gruff; surly; ill-tempered; feisty: Crusty George Meany. The downturned lips, the jowls, the half-closed lids, all were dour (1834+)