The most common and most likely answer to this crossword clue is the 7 letter word DUMBEST
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More clues leading to the result DUMBEST
Buddy explains!

The straight part
We know that "we’re at back!" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case we’re at back! = dumbest.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.
What does DUMBEST mean?
DUMBEST adjective- Unable to speak; lacking power of speech (kept in "deaf, dumb, and blind").
- Silent; unaccompanied by words.
- (especially of a person) Extremely stupid.
- Pointless, foolish, lacking intellectual content or value.
- Lacking brightness or clearness, as a colour.