Synonyms for Goof:

n.

numpty, joker, dumb blond, maniac. gander, tomfool, error, softhead, mix up, nincompoop, nerd, dip, simple, cretin, moron, schmo, turkey, schmuck, simpleton, flaw, nitwit, ability, imbecile, misapprehension, jerk, ding-dong, fool, Mooncalf, ninny. bloomer, bull, slip up, miss, fall short, let down, Foozle, foul up, blooper, correct, trip-up, mess up. laze, loaf, loiter, shirk, idle, industrious, diddle, lounge, goldbrick. blunder (noun)
error, blooper, fluff.
boob (noun)
fathead.
bungler (noun)
bungler, bonehead, clod, clown, clodhopper, dolt, oaf, bumbler, fumbler, yokel, blunder-head, botcher, butter-fingers, blockhead.
dunce (noun)
blockhead, dolt, oaf, moron, imbecile, jerk, nincompoop, simpleton, bonehead, fool, ninny, nitwit.
error (noun)
flaw, misapprehension.
goof (noun)
fathead, goose, sin, zany, bozo, cuckoo, blunder, twat, boob.
schlemiel (noun)
schmuck.
screwball (noun)
bozo.

v.

blow (verb)
fail, miss.
err (verb)
fluff, misestimate, misjudge, misconstrue, blunder, misconceive, trip, slip up, mar, miscalculate, err, slip, botch, bungle, sin, stumble.
goof (verb)
mix up, botch, blunder, miscalculate, flub, bungle, slip, err, mess up, foul up.

Other synonyms:

bloomer, cretin, schmo, ninny, error, nerd, schmuck, softhead, blooper, ding-dong, tomfool, Foozle. turkey, moron, nitwit, Mooncalf, simpleton, nincompoop, imbecile. shirk, fool, loiter, gander. simple. blow
miss.
err
slip, slip up.
Other relevant words:
flaw, flub, fathead, sin, turkey, error, schmuck, lounge, boob, laze, softhead, imbecile, ding-dong, fail, goldbrick, fool, simpleton, nincompoop, bull, schmo, bozo, tomfool, cretin, dip, nitwit, ninny, zany, loiter, nerd, gander, loaf, twat, shirk, goose, misapprehension, idle, cuckoo, moron, simple, bloomer, diddle, jerk, Foozle, Mooncalf, miss, make a mistake, blooper.