Probably the most satisfying noble shut-up in DA for me is... well, I can't even remember his name. If you join the mercenaries in the prologue, in Act 1 your old boss gives you a job to kill a nobleman who ambushes previous mercenaries. He comes out, strutting in his superiority, and you can talk to him... or just pick the murder knife, at which point he quickly realizes that he's about to die, and says something about being avenged by his sons before taking it to the gut.
Not the most insufferable ****** of them all, but it's such a final turn around from 'I was more intelligent and ambushed your fellow' to 'meet the murder knife' that it stands out.
Plus, it's kind of fun to roleplay the attempted revenge assassination attempt later on.
"Hawke, you killed my father!"
"Did I? I kill lots of fathers. Can you give me a hint?"
"He was an important nobleman!"
"Varric, have I killed any important noblemen?"