1. Episodes written by Steven Moffat
that aren't very good for various reasons (sexism, gaping plot holes, story discontinuity, etc).
2. A tag used on Tumblr and other social media sites when complaining about TV episodes Moffat has written which have included a lot of sexism, loopholes, or otherwise poor writing, and has disappointed fans.
Phrase comes from the idea that we don't want to watch episodes where Moffat just wanks himself (as in writes whatever he wants, regardless of the fans, character development, overall story, or preset rules of the story universe like in Doctor Who).
Additional information: Moffat is a Scottish writer who has written for Press Gang, Stay Lucky, Joking Apart, Murder Most Horrid, Chalk, Coupling, Jekyll, The Adventures of TinTin, and, most famously, Doctor Who, and the BBC's Sherlock.
A: That last episode of Doctor Who was some serious moffat wank. Loopholes, much?
B: Yeah, I definitely prefer RTD's episodes lately.