Throw party ending in fornication? Sure thing! (10)
I believe the answer is:
disconcert
'throw' is the definition.
(both can mean to unsettle)
'party ending in fornication? sure thing' is the wordplay.
'party' becomes 'disco' (I've seen this in other clues).
'ending in' suggests the final letters.
'sure thing' becomes 'cert' (as in a dead cert).
The final letter of 'fornication' is 'n'.
'disco'+'n'+'cert'='DISCONCERT'
(Other definitions for disconcert that I've seen before include "Shake up" , "Dismay" , "Bother" , "Throw" , "Disturb, unsettle" .)