A state of relative nothingness, boredom, frustration, or just general existence for which there is no adequate substitute. Merbling can be an action, as well as an adjective, or a general conversation filler, as well as noun (merbler). There are many forms of merble, but all involve similar, unexciting emotions.
"Man, about ten minutes into that 3-hour lecture, I was merbling hard, it only got worse from there"
"Dude, your 30 minutes late!" "Merble!"
"I went on a date with that girl, but she was too much of a merbler, so I bailed."