The actress, who starred for years in Coronation Street, teamed up with EastEnders star Charlie Brooks for the challenge that saw the pair asked to dive under water and pick up stars with their teeth while trying to ignore water spiders, eels and lizards.
Brooks managed to get three stars, but Flanagan ignored hosts Ant and Dec's instructions and picked up four stars with her hands, which meant they did not count.
Explaining herself to the Geordie duo, she said: "I think it's because I panic so much, I forget using my teeth. I did my best."
But her excuses cut no ice with Brooks, who said: "Just the silliness of it all frustrates me. It's like, 'You really need to get a grip sometimes'."
There was also tension between Brian Conley and David Haye after the boxer sparked a row when he flicked two burning logs on to the forest floor.
A furious Conley ended up in tears before he was comforted by Colin Baker.
An apologetic Haye said: "So maybe I've got to be a bit more sensitive, a bit more careful about what I say around him. And then try to pick up his spirit somehow and not do anything that unsettles him."