"Pick a character in any fandom and write their fanfic about their favourite show."
But I realised that I couldn't then share the results with you, so I've posted it here too.
Please spread far and wide, because I think that this has the potential to be bloody hilarious!
lozenger8 has already risen to the challenge with The One With the Thing - Danny from Hot Fuzz writes Life on Mars. And I was right. Bloody hilarious.
nostalgia_lj has written Donna: Beta Reader Angel as written by The Doctor. Absolutely hilarious and so true. Ten is such a Spike/Angel shipper.
grey_bard has written Genius at Work. Sleepy Hollow as written by Abby of NCIS. It's the forensics.
kipli has written Their Fandoms. Various fandoms as written by the Scrubs team. Phear the almighty beta that is Dr. Cox.
hambelandjemima has written Those Meddling Kids. Life on Mars's Sam Tyler apparently wrote Scooby Doo fanfic as a child. Who'da thought it?!
bank_farter has written So Busted. Juliet from Psych is a Scrubs fan.
shebit has written Austen Effulgent. Spike's rather flowery homage to Pride and Prejudice.
dameruth has written How To Get Fifty Hits In Five Minutes, Jack Harkness shows how with the help of the Harry Potter fanfic.
mprice and friend have written: The Emperor Wins, Disciple, and Dungeons & Dorian. Fictional RPF in the From Eroica With Love fandom.
butterflykiki has written Of Anthropological Interest Daniel & Janet, of SG-1, bickering over Xena/Gabrielle fanfic.
fawsley has written The secret notebook of WDC Annie Cartwright. Life on Mars' Annie turns out to approve of The Sweeney's Carter/Regan. Who knew?