One thing I’ve noticed, especially in TV shows that suddenly have a musical episode, is that pretty much all successful actors also have pretty good singing voices. Anyone have any examples of well known actors that are horrible singers? Youtube links even better!
Sarah Chalke, while not awful, was the weakest link in the Scrubs musical episode.
In seeing the recent movie Mama Mia, I couldn’t help thinking that Pierce Brosnan’s singing sounded like an embarrassed frog moaning in pain.
Allison Hannigan was the weakest on Buffy.
The only musical episode I can remember clearly is the Buffy one (Once More With Feeling)…The only good singers in it were Tony Head, James Marsters and Amber Benson - while nobody else was terrible, the rest were pretty weak - I’ll Never Tell is my favourite song on the soundtrack, but the best that can be said about Nick Brendan and Emma Caulfield’s singing is that they’re not painful to listen to. Alyson Hannigan has said she insisted her singing parts be minimal, because she’s not much of a singer.
Speaking of Buffyverse actors, David Boreanaz is a lousy singer - and has no problem with proving that on screen.
Can’t access You Tube…but see if you can find Lee Marvin singing in “Paint Your Wagon.”
Never saw it but I remember hearing that Drew Barrymore got out of singing in Woody Allen’s musical “Everyone Says I Love You” because she said she’s such a lousy singer:
Hm, also notes that Goldie Hawn sang so well that they had her tone it down. 
Supposedly George Clooney tried to do the singing in O Brother Where Are Thou himself, but was so bad that he personally supervised the destruction of the recordings.
I wouldn’t call her well-known now, but she was at the time: Dawn Wells. On the Mosquitoes episode of Gilligan, the three women formed a singing trio to be the opening act for the featured rock group. Tina Louise and Natalie Schaefer sang for themselves, but DW had to lipsynch. It was painfully obvious, but she freely admitted that it would have been far more painful if she had sung for herself.
Apparently he’s tone deaf, but I could just be making that up.
Rex Harrison in My Fair Lady is one of the classic examples of a great actor who can’t sing. But his way of speaking the lyrics has so defined the character of Henry Higgins that it’s difficult for me to imagine an actor actually singing them!
And the Janitor was a surprise, too!
Michelle Trachtenberg did too. It was also her idea to have Dawn perform an extended dance number because while she couldn’t sing, she could dance.
Cameron Diaz can’t sing to save herself.
This is what I came to post.
Ruined the movie for me it did.
Lee Marvin and Rex Harrison are taken? Okay, I’m stuck making a sexist comment.
She sang? rimshot
Okay, it wasn’t THAT sexist, but I came up in the 50s and 60s and standards for sexy/sexist comments were lower. That’s why we needed the rimshots.
Stephen Fry says he’s tone deaf and can’t sing worth a lick. IIRC all of the lines he’s had to sing on A Bit of Fry and Laurie and Jeeves & Wooster he just speaks instead - which is funny.
Which is why all the scenes of Angel singing are hilarious!
I will never understand why people cast Meryl Streep in singing roles. Sure Pierce Brosnan was bad in Mama Mia, but shouldn’t the lead in a musical at least know how to sing?