It's awfully rude to strip outside when threatened (5,6)
I believe the answer is:
under duress
'it's awfully rude to strip outside when threatened' is the definition.
I can't judge whether this defines the answer.
'it's awfully rude to strip outside' is the wordplay.
'it's awfully' indicates anagramming the letters.
'to strip' becomes 'undress' (synonyms).
'outside' is an insertion indicator.
'rude' with letters rearranged gives 'erdu'.
'erdu' placed within 'undress' is 'UNDER DURESS'.
Can you help me to learn more?
(Other definitions for under duress that I've seen before include "Subject to improper coercion" , "Pressured" .)