The most common and most likely answer to this crossword clue is the 2 plus 3 plus 2 plus 1 plus 7 letter word GO OFF AT A TANGENT
G
O
O
F
F
A
T
A
T
A
N
G
E
N
T
Buddy explains!
The straight part
We know that "to talk irrelevantly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case to talk irrelevantly = go off at a tangent.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.