stumblebum       
 noun [ C ] US informal uk/ˈstʌm.bəl.bʌm/ us/ˈstʌm.bəl.bʌm/
 笨头笨脑的人;无用的人
someone who often fails or makes mistakes because they have very little ability or skill
  He might not be such a stumblebum after all - maybe he has talent.  他也许不是这么笨的一个人——可能他也有才华的。 
 - More examples
 - I believe in this guy; he is not a stumblebum.
 - He plays a stumblebum who mangles every sentence.
 - Christopher Plummer's performance as an alcoholic stumblebum in the movie was hailed.
 
stumblebum       
adjective [ before noun ] US informal uk/ˈstʌm.bəl.bʌm/ us/ˈstʌm.bəl.bʌm/
 笨拙的;无用的
often failing or making mistakes because of a lack of ability or skill
  Her stumblebum efforts at childcare make for hilarious viewing. 她在照顾孩子方面笨手笨脚,一系列行为让人看着都想笑。 
 - More examples
 - Not even the most stumblebum troupe of mimes could have put on a funnier show.
 - I lost patience with the film's stumblebum attempts to portray this hypocrite as a martyr and a hero.
 - Will Smith stars as Hancock, a stumblebum boozer who also happens to be able to lift oil tankers and fly through the air.