Wasting time, doing nothing in particular. Also, can mean finding idle tasks to do while wasting time.
Comparable to dilly-dallying.
I'm just faffing about until lunch time.
- What are you doing there, working?
- Nah, I'm just faffing about.
Short form of This Is Why People Kill.
Originated in a reddit thread regarding design, now also a subreddit (r/thisiswhypeoplekill).
There's an unfilled row of pixels below that rectangle. You know, TIWPK.