These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Darcy: You were supposed to be seducing her, but you just looked a little stiff.
Badass Decay: Some series feature a contestant who starts off brilliantly, getting scores usually not seen until the later stages as early as week 3, who then runs out of steam and is usually eliminated before the final. Austin Healy from series 6 and Scott Maslen from series 7 both spring to mind.
Designated Villain: Craig is styled as "the mean one", but will usually try to end on a positive note and can be very nice when he genuinely likes something (the simple "Fab-u-lous!" being the show's most prized accolade). He is in fact many people's favourite judge.
8.8: Alesha Dixon giving her obvious favourite, Harry Judd of Mc Fly, 10 as early as week 4.
Ensemble Darkhorse: John Sergeant in the 2008 series, who set half of Britain on fire with controversy as the public kept voting him back in when the judges...er...strongly criticised him, shall we say.
Chris Hollins, one of 2009's dark horses, won the competition over Ricky Whittle and Ali Bastian, both of whom had been frontrunners since week 1 and were rather more technically skilled (this is not to say that Chris is terrible technically, but he is rather more on the 'performer' side of Technician Versus Performer).
And then there was Christopher Parker, from the first series. Pretty much dire, got into the final anyway. Possibly because he did a Paso Doble in the style of Dracula.
Kelly Brook in the 2007 series; prior to that she had been regarded as quite good looking but utterly talentless by just about everyone in Britain. When she appeared on the show however, she actually proved to be a very good dancer; maybe not good enough to actually win that year's prize (she dropped out near the end of the series after her father died), but her performance was still pretty impressive by any standards.
Chelsee Healey, much like Kelly Brook she had bags more talent than would've been expected, however the judges paid little attention to her as a competitor until relatively late in the contest.
Ho Yay: The male professionals. They're dancers, they can't help it.
Special mention goes to Robin and Artem, who lived together for the 2010 series.
Lest we forget that unexpected moment between Gavin and Bruno in series 8.
Artem and James. Doing the Rumba.
And on the Wembley show in 2011, a VT consisting of Artem being more intrested in dancing recently booted professional, Brendan Cole than his own sexy partner (Holly Valance).
Artem and James again on the Botafogo Challenge final. They came down the ITT stairs holding hands, Artem attempted to hug James twice...let's face it, every time Artem interacts with other male pros, this trope comes into effect.
Tess Daly's flirty presenting style sometimes leads to this with female contestants.
Lowest Common Denominator: People vote for "contestants" who are not good because they are funny or entertaining, despite the fact that the show is sold as a Dance Competition, not an Entertainer Competition.
Gavin Henson got through to the semi-finals, based on... well. Use your imagination.
Portmanteau Couple Name: Tends to happen to the more popular couples; e.g Chris Hollins + Ola Jordan = Cola. They even had matching "Team Cola" t-shirts made up once the name started to catch on.
The Scrappy: Regularly any given series will have at least one pair who are notably sub-par but survive elimination week after week while better dancers get kicked out. While some are saved in the viewers' esteem by being particularly entertaining or charming, individual reactions vary widely. Candidates include Ann Widecombe, John Sergeant, Kate Garraway, Gavin Henson, Nancy Dell'Olio and Christoper Parker.
The Woobie: Craig Kelly in the 2009 series. He lasted one week after one of the better dancers (Zoe Lucker) in the competition had a shocking exit (or not so shocking, considering she was paired with James Jordan, the unluckiest professional ever) and the judges tore him, specifically, to pieces. Even though it wasn't actually his fault that Zoe had left, it was the fault of the voting audience. In his hometown, which he'd been saying for the last four weeks that he would do anything to get to (one of the shows that year was filmed in Blackpool Tower Ballroom).