One who posts non-stop on Tumblr, the blog website. Often talks about his/her latest post or 'reblog'. Similar to the twitter shitter. Can also be full of self-righteousness.
Bumbler: "Yo, Mike, did you see that post of me talking about pointless stuff on my Tumblr this morning?"
Mike: "No, bumbler, and I don't give two shits in a handbasket, you goddamn Tumblr bumbler."
Bumbler: "But, Mike, I'm fucking awesome!"