'crusty' originates from English, specifically formed from the noun 'crust' with the adjectival suffix '-y' (meaning 'having or characterized by'). 'Crust' itself comes ultimately from Latin 'crusta'.

'crust' came into English via Old French 'cruste' from Latin 'crusta', and the English adjective 'crusty' was formed by adding the suffix '-y' to 'crust' in later English.

Initially, 'crusty' primarily meant 'having a crust' or 'covered by a hard outer layer'; over time it developed a figurative sense meaning 'surly' or 'bad-tempered', which is common in modern usage.