In regards to that Sweeney coffin thing... I find stupid symbolism annoying.
"In a play or movie when a character is opening up a present, but instead of unwrapping the paper like a normal person, they simply just lift off the lid."
I ALWAYS notice that too. Drives me nuts.
Okay, this one's really stupid and nitpicky, but here goes: in "Flagmaker, 1776" from Songs for a New World, the woman sings "And his last letter says he's fighting in a ditch." The Revolutionary War used 18th century European style battle tactics; trench warfare didn't come about until the 20th century! Gahhh!
Another historical nitpick. In Parade, Frankie goes off to fight WWI at the end... several years before the USA became involved in it. Yeah.
Phantom of the Opera - Raoul's "ingenious" plan in which he plots how to capture the Phantom, because you know, it's been done so easily before. It not only makes the character look dumb (because he thinks it will work,) it makes the writers look dumb. For that matter, I'm also annoyed with how ALW actually wrote Don Juan which is supposed to be this amazingly awesome opera, and just made it consist of earlier melodies from the show and one ridiculously symbolic pop duet.
Another one from Phantom is the theme song which, while a cool melody, has lyrics that do not fit in with the rest of the show (for instance, Christine sings "Those who have seen your face draw back in fear" when she hasn't seen Erik's disfigurement yet.) That's what you get though for writing the song before the rest of the show, I suppose.
This one I CANNOT stand: "A New Life" in Jekyll and Hyde. Jekyll warns Lucy to RUN FOR HER LIFE. What does she do? She sits there for FIVE MINUTES singing a ballad. The entire time you're like "Run, you idiot! Hyde's after you!" And then, of course, she doesn't get out in time and she dies. I like the song itself, but in the context of the show it's just too much.
Jane Eyre Broadway version - In "My Maker" Jane talks about how she will not be blessed by God because she's harmed the thing that she loves best. Doesn't that completely destroy the point of Jane leaving Rochester because she would be sinning, and therefore she chose God over him? I mean, what the heck?
Miss Saigon - Chris says that Kim cost the price of a Big Mac... but she cost $20-$50. I think it's safe to assume that Chris got overcharged at McDonalds back in the States. Then again, he isn't the brightest: the whole "Oh, we'll totally know ahead of time when the VC are going to come!" thing proves that.
Les Mis - How Valjean escapes from Javert in "Confrontation." I know that they can't do the whole "fakes his death" thing like in the novel, but a chair? SERIOUSLY.
... and I'm going to stop now before I look even more nitpicky.
Jimmy, what are you doing here in the middle of the night? It's almost 9 PM!