The most common and most likely answer to this crossword clue is the 7 plus 9 letter word FLEA IN ONE’S EAR
I've seen this crossword clue in The Guardian
F
L
E
A
Â
I
N
O
N
E
â
€
™
S
Â
E
A
R
Buddy explains!
The straight part
We know that "Summarily dismissed with this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case summarily dismissed with this = flea in one’s ear.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.