Good humor may be said to be one of the very best articles of dress one can wear in society.

Thackeray’s remark treats temperament as a kind of social “attire”: something others immediately perceive and respond to, often more strongly than they do to literal clothing or status. “Good humor” here implies an ease of spirit—kindness, patience, and a readiness to laugh—that smooths social friction and makes one welcome in company. The metaphor also carries a moral edge typical of Thackeray: society is full of performance and display, but the most valuable display is not fashion or wealth; it is a gracious disposition. In that sense, the line is both practical advice for social life and a quiet critique of superficial social values.