Jack gets Rosalie no end upset! (6)
I believe the answer is:
Here is my best explanation:
'jack' is the definition.
'rosalie no end upset' is the wordplay.
'no end' means to remove the last letter.
'upset' is an anagram indicator.
'rosalie' with its last letter taken away is 'rosali'.
'rosali' anagrammed gives 'SAILOR'.
'gets' acts as a link.
(Other definitions for sailor that I've seen before include "One in the main", "10 [MARINER]", "Seafarer", "Old salt", "Mariner", "Sinbad, for example", "Matelot", "Seaman", "Sinbad, maybe" and "Ship's crew member".)