Existential dread's stopping German hoodlum (8)
I believe the answer is:
gangster
'hoodlum' is the definition.
(I've seen this before)
'existential dread's stopping german' is the wordplay.
'existential dread' becomes 'angst' (I've seen this in another clue).
'stopping' indicates putting letters inside (inserted letters stop or plug a gap).
'german' becomes 'ger' (abbreviation).
'angst' inserted inside 'ger' is 'GANGSTER'.
(Other definitions for gangster that I've seen before include "Member of a mob like Al Capone" , "Soprano possibly" , "Hoodlum" , "Member of criminal mob" , "Mafia man" .)