en pan|tou|fles

en pan|tou|fles «ahn pahn TOO fluh», French.

1. in slippers: »

Then came the French, shuffling along as if en pantoufles (New Yorker).

2. Figurative. easy, casual, or informal: »

The authority and erudition he can pack into eight pages on “The North-East in the Eighteenth Century,” for instance, is yet one more proof that he is never en pantoufles (London Times).