There isn't much the Pitch Perfect star won't do on camera for the sake of comedy, including grossly over-the-top kissing scenes, crazy drunk antics and wearing embarrassing costumes, but she isn't comfortable going nude for a movie and opted for a body double for her recent film Grimsby.
"They wanted full-frontal nudity. We write in the contract, specifically, 'No nudity,'" she told Britain's Marie Claire magazine. "They got in another girl - this larger burlesque dancer from South Africa - to be a nude double. And they got her to do all this stuff."
Her co-star Sacha Baron Cohen, who also co-wrote and produced the comedy, pointed out to Rebel that the double looked good, as if hinting for her to have a go, but she continued to refuse.
"I'm like, I'm not doing it. I don't care what you say,'" she recalled.
Rebel admits she could be persuaded to do it if it was a serious film but the crew on comedies don't tend to have the "sensibility and decency" needed for her to feel comfortable stripping off.
The 36-year-old star has become one of Hollywood's hottest names, but only attended community acting classes as a child because her mum wanted to help her get rid of her crippling shyness, which was "bordering on a social disorder", but Rebel really didn't want to go.
"So my mum - one day she drives me to this community acting class," she recalls. "I was holding on to the car door and crying. She had to peel me off the car. She's like, 'I'll pick you up in two hours,' And she left me."