The most common and most likely answer to this crossword clue is the 6 letter word NOONER
N
O
O
N
E
R
Buddy explains!
The straight part
We know that "lunchtime mischief in DC" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lunchtime mischief in dc = nooner.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 NOONER mean?
NOONER noun- A sexual encounter during lunch hour, especially one which is illicit.