As best I could make out, having never heard the term until I arrived in California, being a WASP meant being mossbacked, lockjawed, rigid, humorless, cold, charmless, insipid, less than penetratingly bright, but otherwise---and inexplicably---to be envied.
Kay Redfield Jamison (2014). “An Unquiet Mind: A memoir of moods and madness”, p.26, Pan Macmillan