Well, mine go out and about all the time, so this is an issue I deal with all the time.
I control other people's interaction with my birds. No exception. And mine have been bite pressure trained, and socialized to the Nth degree. They pinch, they don't draw blood. No damages = no basis for an award.
Finally, AND THIS IS THE MOST EFFECTIVE WAY I'VE FOUND TO GET THE POINT ACROSS. I keep part of a toy in the car. It's a block of wood that Maggie bit in half... BEFORE anyone approaches my bird, I hand them the broken toy, and ask them to squeeze it until it shatters. Obviously, the answer is, I can't do it...
Then I tell them that I make her toys out of this stuff. SHE CAN! Then I take that block of wood, and compare it to my arm. The toy is THICKER...
Enough said. Now, she is tame, BUT sometimes she doesn't want strangers touching her. So if she says NO TOUCHING, it means NO TOUCHING!! Understand?!
I've been taking birds out and about for fifteen years now, never had an incident - except with an attempted bird thief who tried to grab a macaw out of a tree in the park, and run off with her....
TRUST ME - HE WON'T DO THAT AGAIN!!!