Lovelorn cowboy on lake shows tactless behaviour (9)
I believe the answer is:
gaucherie
'tactless behaviour' is the definition.
(socially awkward behaviour)
'lovelorn cowboy on lake' is the wordplay.
I cannot quite understand how this works, but
'lake' could be 'erie' (Lake Erie is one of the Canadian/US 'Great Lakes') and 'erie' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'shows' is the link.
(Other definitions for gaucherie that I've seen before include "Tactless behaviour" , "Awkwardness" , "clumsy behaviour" , "Slip" , "Socially awkward acts - huge Erica (anag)" .)