(n, one word) Anyone whose primary assigned job tends to involve using a mop, or cleaning things. Often meant to degrade that person, especially when that person was actually hired or trained to do a much more
complicated job. Used most frequently to describe Navy personnel (as an
alternative to "swabbie") to whom this has happened, since it happens there with startlingly
high frequency.
"
The Navy spent 12 months training me to fix radars, then when I got to my boat, they sent me to
the mess decks, and since
I don't know how to cook, they made me a mopjockey. I get to swab decks all day. Whoopie. Glad I joined."