How can i ask somebody if i can stop using honorifics towards them?
For example when I become familiar with somebody how can I ask "May I stop using honorifics?"

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Ok, I found that : 
http://ko.wiktionary.org/wiki/%EB%B0%98%EB%A7%90 
On the page, there's this sentence : "이제 우리 서로 반말을 쓰죠." 
("We will use 'banmal' from now, ok?")

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우리 말 놔요

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Again, not 100% sure (since I'm not a native)

반말해도 돼요? Can I/we use "banmal"? 
 
반말해도 될까요? It would be ok to use "banmal"?

반말로 할까요? Should we talk in "banmal"? You don't want talk in "banmal"?

반말로 하는 게 어덜까요? What about talking in "banmal"?

Answer

In general someone will ask you to use their first name, or you can say "Do you mind if I call you xxxx".