The most common and most likely answer to this crossword clue is the 4 plus 3 plus 5 letter word COME OFF WORST
I've seen this crossword clue in The Daily Telegraph
C
O
M
E
O
F
F
W
O
R
S
T
More clues leading to the result COME OFF WORST
Buddy explains!
The straight part
We know that "it’s what losers do" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it’s what losers do = come off worst.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.