The most common and most likely answer to this crossword clue is the 4 plus 3 plus 4 plus 4 letter word HAVE TWO LEFT FEET
I've seen this crossword clue in The Sunday Telegraph
H
A
V
E
T
W
O
L
E
F
T
F
E
E
T
More clues leading to the result HAVE TWO LEFT FEET
Buddy explains!
The straight part
We know that "to be a terrible dancer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case to be a terrible dancer = have two left feet.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.