WordNet (r) 3.0 (2006):

muck up
    v 1: make a mess of, destroy or ruin; "I botched the dinner and
         we had to eat out"; "the pianist screwed up the difficult
         passage in the second movement" [syn: botch, bodge,
         bumble, fumble, botch up, muff, blow, flub,
         screw up, ball up, spoil, muck up, bungle,
         fluff, bollix, bollix up, bollocks, bollocks up,
         bobble, mishandle, louse up, foul up, mess up,
         fuck up]
    2: soil with mud, muck, or mire; "The child mucked up his shirt
       while playing ball in the garden" [syn: mire, muck,
       mud, muck up]

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "muck up":
   ball up, begrime, bemire, bemud, besmoke, bloomer, blooper, blow,
   bobble, bollix, bollix up, bonehead play, boner, boo-boo,
   boob stunt, boot, bugger, bugger up, complicate, confound, confuse,
   cook, dirt, dirty, dirty up, drop a brick, drop the ball, duff,
   dumb trick, dust, embrangle, entangle, fluff, fool mistake, foozle,
   foul up, foul-up, fumble, garble, goof, grime, gum up, hash up,
   howler, implicate, involve, jumble, knot, louse up, louse-up,
   mess up, mire, mix up, muck, muddle, muddy, perplex, pi,
   play hell with, play hob with, pratfall, pull a boner, queer,
   ramify, ravel, riffle, scramble, screamer, screw up, screw-up,
   shuffle, sink, slime, smoke, snafu, snarl, snarl up, soot, tangle,
   tumble