The loanword de rigueur, meaning socially obligatory, proper, or required by custom, functions as an adjective in English. It comes from French, where it means, literally, of rigor and, less literally, according to strictness. De rigueur is also a common expression in that language, where it means roughly the same as in English.
De rigueur has been in English a few centuries, so it does not have to be italicized in normal use (we italicize it here because it is presented out of context). But many publications italicize it anyway.
In English, the phrase is usually pronounced duh ri-GUR—with the accent on the last syllable.
With bribery and corruption de rigueur there are very few arms transactions that are entirely above board. [Guardian]
I know that Corned Beef and Cabbage are practicallyde rigueur for the feast of St. Patrick. [A Continual Feast… Continued!]
Public attitudes about fat have never been more judgmental; stigmatizing fat people has become not just acceptable but, in some circles, de rigueur. [NY Times]
But for some unknown and definitely ungodly reason, lack of trousers appears to be de rigueur. [Stuff.co.nz]