Put your foot in it, in a manner of speaking? (6)
I believe the answer is:
strain
'a manner of speaking?' is the definition.
(thesaurus)
'put your foot in it in' is the wordplay.
'foot' indicates one should take the final letters (in a down clue, the bottom letter).
'in' indicates putting letters inside.
'it' becomes 'sa' (old-fashioned abbreviation for sex appeal).
The last letters of 'put your' are 'tr'.
'tr' placed within 'sa' is 'stra'.
'stra'+'in'='STRAIN'
(Other definitions for strain that I've seen before include "Race" , "Violent effort" , "Family; effort" , "Blood" , "Make intensive effort" .)