You're going to do a demo of a network connected device in a new place? Bring your own network. If you can bring all the parts with you, that's even better -- a self-contained system that has no external dependencies is best.

If you absolutely need network connectivity, bring a cellular-wifi hotspot that you've already tested. Talk to the site organizer to find out what cell networks work there, and if you need to, buy a SIM in advance.

If you don't have an IT organization, you are the IT organization, so be a good one.

While I emphatically agree with you, if the person doesn’t know what they are doing, following your advise can cause major havoc too.

As someone who has hosted hack days in many countries on six continents and prides himself on providing a reliable and friendly network (including hand-on supporting IoT folks) for said events, it’s really freaking annoying when someone starts blasting their AP at ridiculous power levels for their one-off use case effectively muddying to hell the RF spectrum of the event space.

So you were the site organizer, and I bet you told people in advance what they could expect to be available on-site, right?

They weren't in the wrong for being prepared, but for not listening to you.

Irregardless if we were prepaired for them or not, or if they listened or not, there should be an expectation that you know how to use the gear you bring if you bring your own gear.

It’s the equivalent of bringing a machine gun to a shooting range and spraying bullets all around you (missing everyone, but still causing a bad time for all involved) because you don’t even know how to hold it properly.

I swear you only got downvoted here for using the word 'irregardless'