Someone who is sitting around doing nothing.
When playing a video game such as Super Smash Brothers, you have a chance of getting a lumb digger as a partner. While playing your partner isn't doing anything to help you, while you are being thrown off the edge. This ultimately results in you losing or your partner stealing your lives because they died too fast.
During a game of Smash Brothers 2 Vs. 2. Mark and Dan were holding me off the edge, while Aaron Murray was trying to open a box then a barrol. I shouted, "Aaron Murray you are such a lumb digger!"