When a parent is unknowingly cockblocking their kid by being home. The parent is at home, leaving the kid and his girlfriend with no place to get it on. Therefore the parent is obliviously cock blocking.
Matt's Friend: "Yo Matt, did Katie come over last night?"
Matt: "Yeah, but my parent were being complete obliviouscock blockers!"
A person, often otherwise intelligent, who routinely exhibits a comical lack of understanding in social situations.
Such a person is typically well-known for their repeated well-meaning tactlessness, failure to notice romantic overtures, tendency to walk into doorknobs and general forgetfulness.