The most common and most likely answer to this crossword clue is the 3 plus 3 letter word BAD EGG
I've seen this crossword clue in Financial Times
B
A
D
E
G
G
More clues leading to the result BAD EGG
- Rogue ordered two grand.
- Good-for-nothing ordered goods
- Crook offered goods
- Villain demanded to ride horse
- Wished to knock stuffing out of grinning reprobate
- The swine ordered goods
- 1 Bare-legged, perhaps, avoiding ugly leer of despicable person
- Rogue commanded galleons originally
- Black sheep that may float
- Rat that shouldn’t go in an omelette!
Buddy explains!

The straight part
We know that "reprobate" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case reprobate = bad egg.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.