Encourage coitus, wearing nice pants (6)
I believe the answer is:
incite
'encourage' is the definition.
(I've seen this before)
'coitus wearing nice pants' is the wordplay.
'coitus' becomes 'it' (I can't explain this - if you can you should give a lot more credence to this answer).
'wearing' is an insertion indicator.
'pants' is an anagram indicator (UK informal term for 'nonsense' or 'rubbish').
'nice' with letters rearranged gives 'ince'.
'it' going within 'ince' is 'INCITE'.
Can you help me to learn more?
(Other definitions for incite that I've seen before include "Egg on" , "Move to action" , "Urge (to violence)" , "Foment or arouse" , "'Stir up, provoke (6)'" .)