Odd this, why do people feel the need to open an address to a group of people by addressing them by what gender they think they are? I do a lot of workshops etc to groups of individuals ranging from the young to the quite senior and crusty, and I never feel the need to tell them what gender or old fashioned elitist term I think they are! So I never start with "Ladies and Gentleman" nor do I address them as "guys" or "boys and girls."
A simple "Good morning/afternoon/evening" as appropriate, then I introduce myself and welcome them to the workshop/event/speech etc. Then you are away with the event and it is not a problem.
Simple. No one offended.
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