Bruno Tonioli falling off his chair. Happens again in Series 13.
Mark Ramprakash managing to get Karen's microphone wire wrapped around himself 10 seconds into the dance, necessitating a do-over.
Debbie McGee does a Tango to I Gotta Feeling. Craig's reaction when he's asked to say something as a judge is to get up and bow at her feet. When he (and the other four judges), give her a ten each, Darcy's reaction is to grin and tap his shoulder as if saying "well done".
Week Eleven of the 2017 series: Alexandra Burke and her partner, Gorka, dance to Supercalifragilisticexpialidocious - in the dark, in the background, we can briefly see Shirley and Bruno dancing along like crazy mad people in time with her and both are having the absolute time of their lives. They continue this dancing throughout the judges comments.
Another one from the 2017 series: following Mollie King and AJ Pritchard's Quickstep to The Baseballs' version of "Umbrella" being awarded a 9 from Bruno, everyone in the Clauditorium starts clapping and chanting for the pair to kiss, which leaves them visibly flustered.
Claudia: They're all shouting "kiss"... We'd all like it, but... Okay, we'll wait 'til the wrap.
And then one week later, after the pair was saved from elimination during Musicals Week...
AJ:[to Mollie] You're willing to train, for over 300 hours!
Claudia: Very good, and only half of that time is spent kissing. I'm joking.
[Mollie starts laughing as the audience and the other contestants in the Clauditorium reacts in amusement]
Claudia: I'm joking! I'm joking!
Gemma and Aljaz: Kiss! Kiss! Kiss!
The following conversation occurs in the 2017 Christmas Special after Jeremy Vines dances and the judges are giving their scores - it involves Craig, a changing of scores and Darcy looking like she is going to kill someone.
Darcy:(dropping all composure and literally vaulting to her feet): OH!
Craig:(Craig stares up at her in shock as she literally shoves him.) Darcy!
Darcy: GOD SHAME THAT! You can't say that! It's Christmas!
Craig: Oh, sit down, darling.
Darcy:(literally shrieking)IT'S CHRISTMAS!
Craig:(As Darcy sits down, rather angrily). Oh, alright, hang on. (He rummages through his numbers and changes it to a...) Seven. It's Christmas.