The most common and most likely answer to this crossword clue is the 6 letter word WEEPER
I've seen this crossword clue in The Guardian
W
E
E
P
E
R
More clues leading to the result WEEPER
Buddy explains!

The straight part
We know that "Proverbial loser" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case proverbial loser = weeper.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 WEEPER mean?
WEEPER noun- A person who weeps.
- A hired mourner.
- A pleurant.
- A thing that slowly leaks liquid.
- A weeping tree.
- A white border round the sleeve of a mourning dress.
- A crape hatband.
- A widow's crape veil.