Somebody who is retarded three times over. An exceptionally stupid person. Derived from "triple" meaning three, and "Mongoloid" meaning retard.
"she is so fucking dumb she must be a triplegloid."
"My neighbors got beat up by the cops for being triplegloids last night"
"Bob's such a triplegloid that when God was handing out brains, he thought he said "trains" and missed out on his"