Blagh is the Umbrian reflex of the Greek βλωγοσ, both ultimately from Indo-European *bʰleh₁-, “to blow, be vapid; to be wrong on the internet.”

tanadrin.tumblr.com/post/62173…

via allthingslinguistic.com/post/6…

please read the whole post (if interested in #linguistics, of course), it's worth doing so (and pretty short anyway)