[MR4D]

The only way I've found to protect against this is by being paranoid.

Whenever someone asks for my boarding pass, I show them my phone, while the paper copy is safely in my pocket.

[strictnein]

I've always printed two boarding passes and kept them in my carry on. I've had gate agents walk away with my boarding pass in the past and simply never return.

[hamami]

yes I've thought about this as well after the event, now I keep a printed copy in my pocket and use the one on my phone in case something like this happens again (on a different airline)