Dude getting rude ultimately causes shock (4)
I believe the answer is:
mane
'shock' is the definition.
(both can mean a mass of hair)
'dude getting rude ultimately' is the wordplay.
'dude' becomes 'man' (dude can informally mean a man).
'getting' says to put letters next to each other.
'ultimately' indicates one should take the final letters.
The last letter of 'rude' is 'e'.
'man'+'e'='MANE'
'causes' is the link.
(Other definitions for mane that I've seen before include "Long shaggy hair" , "Long flowing hair" , "(Lion's) hair on neck" , "Hair (of lion)" , "Animal's neck hair" .)