No problem it is there choice but first of all we need to be happy ....

Be direct. Some religions push the need to convert and the more "lost" you seem, the harder the push to "save" you. As such, most see being Atheist/Agnostic as being as lost as one can be. If the person is a close enough friend that they deserve an answer, suggest having a sit down where you both explain one time what your positions are, then agree to leave things alone. If that person is not so close, then you owe them nothing and just tell them to stop. Good luck!

Wow. I've known many Muslims while living in the Bay Area. Never known one to "witness" or knock on doors for their religion.

You have a tough spot there. Your best bet is to talk to them about becoming Catholic. You will never be left in peace otherwise. Sometimes it isn’t so important to speak your beliefs as it is to survive the conversation.

Please forgive me if I misunderstood the question but:

I think proselytization from believers in various religions will happen regardless of what is said; it's common that they're told to go out and bring other into their faith. That said whenever anyone tries proselytizing to me I try to at least tell them "no thank you" nicely..... but once they persist I have no issues being rude to them (the best way to combat any religion is to know their texts as good or better than the followers and use their own texts to point out how silly their beliefs actually are)