The most common and most likely answer to this crossword clue is the 9 letter word TREPANNED
I've seen this crossword clue in The Guardian
T
R
E
P
A
N
N
E
D
Buddy explains!

The straight part
We know that "bored in theatre" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bored in theatre = trepanned.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 TREPANNED mean?
TREPANNED verb- To create a large hole by making a narrow groove outlining the shape of the hole and then removing the plug of material remaining by less expensive means.
- To use a trepan; to trephine.
- To ensnare; to seduce, to trick.