[1] : The Collaborative International Dictionary of English v.0.48

mess up \mess up\, v. t.
   1. to make a mess5 of; to confuse, disorder, or muddle; to
      muss; to jumble; to disturb.
      pjc

   2. to botch3; to bungle.
      pjc

[2] : WordNet (r) 2.0

mess 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,
           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, fuck up
     2: disturb the smoothness of; "ruffle the surface of the water"
        syn: ruffle, ruffle up, rumple
     3: make a mess of or create disorder in; "he messed up his
        room" syn: mess
see also:
botch 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 
fuck up ruffle ruffle up rumple mess 

[3] : Moby Thesaurus II by Grady Ward, 1.0

91 moby thesaurus words for "mess up":
   ball up, befoul, benasty, bitch, bitch up, blur, bobble, bollix,
   bollix up, bonehead into it, bugger, bugger up, clutter,
   complicate, confound, confuse, contaminate, cook, corrupt, damage,
   defile, deform, derange, disarrange, disarray, discompose,
   dishevel, dislocate, disorder, disorganize, distort, disturb,
   drop a brick, embrangle, entangle, flub, fog up, foul, foul up,
   goof, goof up, gum up, hash up, implicate, infect, involve, jumble,
   knot, litter, louse up, mar, mess, misarrange, mix up, muck,
   muck up, mucker, muddle, muff, muss, muss up, nasty, obfuscate,
   obscure, perplex, play hell with, play hob with, pollute, queer,
   ramify, ravel, ruffle, ruin, rummage, rumple, scatter, screw up,
   sink, snafu, snarl, snarl up, spoil, sully, taint, tangle, tarnish,
   tousle, unform, unsettle, unshape, upset

Ball Up >> B Words
Ball Up, definition of term: Ball Up
ball+up_pag1.html

Bang Up >> B Words
Bang Up, definition of term: Bang Up
bang+up_pag1.html

Backed Up >> B Words
Backed Up, definition of term: Backed Up
backed+up_pag1.html

Back Up >> B Words
Back Up, definition of term: Back Up
back+up_pag1.html

Ante Up >> A Words
Ante Up, definition of term: Ante Up
ante+up_pag1.html

Act Up >> A Words
Act Up, definition of term: Act Up
act+up_pag1.html