The most common and most likely answer to this crossword clue is the 13 letter word IMPERSONATION
I've seen this crossword clue in The Times
I
M
P
E
R
S
O
N
A
T
I
O
N
Buddy explains!
The straight part
We know that "Act of taking someone off" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case act of taking someone off = impersonation.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 IMPERSONATION mean?
IMPERSONATION noun- The act of impersonating