"Ugh!" (4)
(Other definitions for rude that I've seen before include "Lacking civility" , "lacking refinement" , "Impolite or vulgar" , "'Bad-mannered, discourteous (4)'" , "Impolite - obscene" .)
(Other definitions for icky that I've seen before include "Revolting" , "Nasty, unpleasant (colloq.)" , "Rotten - unpleasantly gooey" , "Cloying -- repulsive" , "Repulsively sentimental" .)
'ugh' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for yuck that I've seen before include "Ugh!" , "Exclamation of disgust" , "Expression of disgust; rhymes with male deer" , "Disgusting (interj.)" , "That's disgusting!" .)