Open with bad pun about bad war (6)
I believe the answer is:
unwrap
'open' is the definition.
(I've seen this before)
'bad pun about bad war' is the wordplay.
'bad' is an anagram indicator.
'about' indicates putting letters inside.
'bad' indicates anagramming the letters.
'pun' is an anagram of 'unp'.
'war' anagrammed gives 'wra'.
'unp' going around 'wra' is 'UNWRAP'.
'with' acts as a link.
(Other definitions for unwrap that I've seen before include "Take the covering off, a parcel say" , "Remove packaging from" , "Reveal" , "Remove the covering from" , "Open (a gift)" .)