The most common and most likely answer to this crossword clue is the 8 letter word WANTONLY
I've seen this crossword clue in Financial Times
W
A
N
T
O
N
L
Y
More clues leading to the result WANTONLY
- Need just showing self-indulgence
- Desire, just in a promiscuous way
- Shamefully desire no more than …
- Desire purely, or in a lewd way?
- Pale boy drinking last of mescal in careless manner
- Need to be without others, showing malice
- Express desire but in an irresponsible way
- Demand nothing but in an extravagant way
- Deliberately ask for limited requirement
- Desire just carelessly
Buddy explains!

The straight part
We know that "in careless manner" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case in careless manner = wantonly.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 WANTONLY mean?
WANTONLY adverb- In a wanton manner.