The most common and most likely answer to this crossword clue is the 7 letter word CRYBABY
I've seen this crossword clue in The Daily Telegraph
C
R
Y
B
A
B
Y
More clues leading to the result CRYBABY
Buddy explains!

The straight part
We know that "Regular howler" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case regular howler = crybaby.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 CRYBABY mean?
CRYBABY noun- A baby who cries excessively.
- Someone whose feelings are very easily hurt, often by trivial matters.
- Someone who takes offense or excessively complains when things aren't going well.