The most common and most likely answer to this crossword clue is the 6 letter word RIBALD
I've seen this crossword clue in Financial Times
R
I
B
A
L
D
More clues leading to the result RIBALD
- Mean guy confronting lad in trouble
- Train regularly plain blue
- To tease a lord is obscene
- Coarse part of biscuit?
- Regularly rail, plain coarse
- Coarse kid, lad with heart in wrong place
- Bridal shower’s hilariously rude
- Architects presented with line drawing originally blue
- Coarse knitting stitch used by a beginner finally unravelled
- Make fun of a learner? Daughter’s mean
Buddy explains!

The straight part
We know that "Coarse" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case coarse = ribald.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 RIBALD mean?
RIBALD noun- An individual who is filthy or vulgar in nature.
- Coarsely, vulgarly, or lewdly amusing; referring to sexual matters in a rude or irreverent way.