Green’s Dictionary of Slang

smug up v.2

[smug v. (6)]

to hide oneself away; to lead an uneventful life.

[UK] ‘’Arry on the ’Oliday Season’ in Punch 16 Aug. 74/1: Could stars of Mayfair be content / To round upon Rome or the Riggi, and smug up in Surrey or Kent?