Ezayyak ya pasha? 3amel eeh? ahlan wasahlan lil montada *
I lived in Egypt (6 October City) for more than a year. Used to drive to Cairo at least twice a weak, hell of a city
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Regarding your dilemma, if you're a close to the family member I think you really are in a tight spot. My advice would be to do everything you can to avoid doing it. Just make up any excuse you can.
If you're not that close, just say you appreciate his trust and stuff but you can't do it.
I have to say, I really respect you for valuing the importance of the ceremony to your friend even though you yourself don't give a shit about religion. That's class
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I hope other members would help you come up with better excuses.
*Translation from Egyptian Arabic (what's up boss? how are you doing? weclome to the forum)