Ruin everything (5)
I believe the answer is:
total
I believe this clue is a double definition.
'ruin' is the first definition.
(total can mean to totally ruin something)
'everything' is the second definition.
(I've seen this in another clue)
(Other definitions for total that I've seen before include "Absolute; sum" , "to give the final figure" , "Come to" , "Full, entire amount" , "final answer" .)