9. Arnold Schwarzenegger - Terminator Salvation
There's little denying that the Terminator franchise is an abject mess these days, though star Arnold Schwarzenegger has generally been pretty diplomatic about the series, keeping his mouth shut about its less-successful sequels.
With the exception, that is, of the fourth film in the franchise, Terminator Salvation.
Salvation remains the only one of the six Terminator films that Schwarzenegger didn't star in, due to his serving as Governor of California at the time.
Instead, Arnie agreed to license to likeness to the production, such that his T-800 character could make a brief cameo through CGI trickery, with Schwarzenegger's 1984 appearance being digitally drafted onto a stunt performer's body.
The results were hugely divisive with the fanbase, to say nothing of the entire film itself, which was largely deemed a missed opportunity by critics and fans alike.
It remains the second-worst reviewed film of the series (behind its sequel, Terminator Genisys), and the second-lowest-grossing (after the most recent sequel, Terminator: Dark Fate).
During a 2015 interview with Good Morning America to promote Genisys, Arnie bluntly gave his opinion on Salvation: "It sucked."
One suspects the actor wouldn't have been quite so honest had he actually physically appeared in the film, because by disparaging the only project he didn't star in, he basically incentivised his own inclusion in future installments.
Seemingly realising the series was missing its special sauce without him, Schwarzenegger was invited back for both subsequent sequels and was the best part of both.