This troper thinks that Mark Corrigan, of all characters, has quite an unexpected Crowning Moment in Peep Show Series Three. After pretending to take ecstasy and being subjected to the ramblings of Jez's druggie friends, Mark goes on a (quite justified) rant about "economic stability, interest rates, growth. It's not all a conspiracy to keep you in little boxes, alright? It's only the miracle of consumer capitalism that means you're not lying in your own shit, dying at 43 with rotten teeth. And a little pill with a chicken on it is not going to change that. Now come on... fuck off." I cheered.
Mark rescuing Jeremy from the book group and tearing Jeremy's love interest's boyfriend to pieces in the process in series 7 -
"...savage rhapsody? Sorry Ben - very easily done - but I think you might accidentally be giving opinions from quite a well known online essay on Wuthering Heights as your own." One of the most awesome things I have ever seen in my life. The second I saw Mark appear at the door I knew what I wanted to happen, and contrary to usual Peep Show form it actually did! Only for Jez to go and squash the moment about a minute later - "Kenneth is what Mark calls his nine inch dildo"
Mark and Jeremy each get their own crowning moment in the series 7 Christmas Episode. Jeremy "resists something for something else" - a quiet hump with Mark's sister - for the sake of his religion, Christmasism: the belief in the sanctity of Christmas. Meanwhile Mark turns what could have been his dethroning moment - being unable to muster the words to defend his girlfriend from his bigoted, bullying, controlling father - into a Moment of Awesome by feeding his Dad's Christmas dinner into a shredder and then giving his Mum and sister the chance to do what they want for a change, while his Dad goes to sulk in the kitchen...
Mark gets an in-universe one in the Season 2 Finale. After Jeff has unexpectedly dropped in on a date and is making the situation awkward, Mark confronts him. Jeff asks, "What are you going to do?" and Mark says he will wait for him to do the civilized thing and leave. Mark undercuts it by narrating that he looked like he was going to hit him but was going to use Sam, the Buddhist, as a human shield.
Jeremy seems to consider Mark getting a Crowning Moment of Awesome in the first episode of series 5, when Mark prevents him from getting out of the flat by tackling him on the floor.
Jeremy: My God, you are! You are fighting me! This is incredible! [while Mark rather gently lowers him on the floor] You're putting your foot behind me, and you're pushing me down towards the floor! [as Mark sits on him] Finally, you're restraining me!
Mark: Okay. All right. I'm not gonna hurt you, I'm just gonna keep you here until the police arrive, okay?
Jeremy: This is - why hasn't this happened before?!
Dobby gets one in the Season 5 episode "Jeremy's Broke." After Jeff mean-spiritedly insults Mark, she stands up to him by doing a silly dance and singing, "Jeff's doing a joke! Jeff's doing a joke! Everybody quiet cause Jeff's doing a joke!" Jeff's only response is to call her "freak" and walk away. Also doubles as a Crowning Moment of Heartwarming.