The most common and most likely answer to this crossword clue is the 2 plus 4 plus 4 plus 1 plus 4 plus 7 letter word GO DOWN LIKE A LEAD BALLOON
I've seen this crossword clue in The Times
G
O
D
O
W
N
L
I
K
E
A
L
E
A
D
B
A
L
L
O
O
N
Buddy explains!
The straight part
We know that "Bomb" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bomb = go down like a lead balloon.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.