Seth Rogen and Evan Goldberg were ''amused'' by the cameos in 'This is the End'.
The duo co-directed the new apocalypse-themed comedy - with Rogen starring alongside James Franco - and thought it would be funny to see a host of stars, including Rihanna and Emma Watson, make brief appearances poking fun at themselves.
Goldberg told The Hollywood Reporter: ''This is the most meta thing we've ever done. It's just really amusing to us to kind of peel things apart and the idea of people playing themselves - and the mere fact that all these guys were willing to actually go at themselves as hard as they do - it tickled us in all the right ways.''
As well as directing, Rogen and Goldberg wrote the film's script, however, they allowed for plenty of improvisation from the actors on set to make the film even funnier.
Co-star Danny McBride explained: ''These guys wrote a great script and they're kind enough to let you just go in there and rip on it and do whatever you want with it. It can be tricky when you have that many people in there improv-ing, but somehow it just worked out; everyone was just very giving.''