The most common and most likely answer to this crossword clue is the 8 letter word CYBERSEX
I've seen this crossword clue in The Guardian
C
Y
B
E
R
S
E
X
Buddy explains!
The straight part
We know that "PC getting off" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pc getting off = cybersex.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 CYBERSEX mean?
CYBERSEX noun- A virtual sexual encounter in which two or more persons connected remotely via a computer network send one another sexually explicit messages simulating a sexual experience.
- To exchange explicit sexual experiences online via text or multimedia.
- To engage in sexual activity, usually masturbation, while communicating online with another person.