Re: Cultural question for my Egyptian friends.
To answer your question of it being offensive, I think not. I am Christian Lebanese and you will definately not offend anyone in my background with hookah use, in fact it would be a great icebreaker in making friends. With that being said, some Christian Egyptians I know are orthodox and very strict with aspects to their religion, more than other Middle Eastern Christians. You can always feel free to ask them since not all people of any religion act the either the way the are supposed to or the way you would perceive them to. Just go ahead and say hi, ask them if they smoke, or just light up. I assume you live in the US, it's a free country and I'm sure they understand that. I think you are worried too much, and you may make some good friends/neighbors out of this, good luck.