Ruin miserable trip (8)
I believe the answer is:
downfall
'ruin' is the definition.
(I know that ruin can be written as downfall)
'miserable trip' is the wordplay.
'miserable' becomes 'down'.
'trip' becomes 'fall' (trip can mean to fall over).
'down'+'fall'='DOWNFALL'
(Other definitions for downfall that I've seen before include "burst of rain" , "Failure (after successful career?)" , "Loss of power or prosperity, a serious tumble" , "Collapse, ruin" , "Cloudburst" .)