The origin of this adjective surprised me. And I thought, in my own armchair psychologist kind of way, that it was interesting that the meaning would have shifted by the time of the Victorian era, to cover anything that is "glaringly conspicuous" -- for, in a time and place when inconspicuousness was mandated by extreme moral compunction, it must have been truly offensive and vulgar, to be so glaringly conspicuous.blatant
1596, in blatant beast, coined by Edmund Spenser in "The Faerie Queen" to describe a thousand-tongued monster representing slander, probably from L. blatire "to babble." It entered general use 1656, as "noisy in an offensive and vulgar way;" the sense of "obvious, glaringly conspicuous" is from 1889.
-Tim