When Ed Harris decided that producing, directing, and starring in Appaloosa wasn't enough for him, and he needed to co-write and sing the movie's theme song ("You'll Never Leave My Heart") over the credits, it was a painful, but endurable, event. The song includes lyrics such as these (he's referring, rather ungallantly, to co-star Renee Zellweger's character)
Being scared and lonely, acting so darn loose
Screwin' who you want to and believing you're excused
and Harris's singing voice might be charitably described as unmemorable. But listening to the song is not an existentially scarring experience.
The same cannot be said of what I just underwent at a screening of Clint Eastwood's Gran Torino. Like Harris with Appaloosa, Eastwood produced, directed, and starred in the film, and like him, he co-wrote and sang the song ("Gran Torino") that plays as the credits roll. Unlike Harris though, his performance could not, even charitably, be described as "unmemorable." See if you can make it to the part where he sings that his heart is "locked in a gran torino. It beats a lonely rhythm all night long." This is William Shatner "Rocket Man" territory we're entering, but much, much less enjoyable.
And, yes, I know that technically a trend is supposed to require three instances. But there was no way I was going to wait until Sly Stallone mumbled his way through the theme to Rocky Balboa Returns before speaking out.