Stare. It seems to upset them.
I do that. Always. They especially hate it on airplanes. But probably not half as much as I hate seeing them on there.
"A strict observance of the written laws is doubtless one of the high duties of a good citizen, but it is not the highest. The laws of necessity, of self-preservation, of saving our country when in danger, are of higher obligation. To lose our country by a scrupulous adherence to written law, would be to lose the law itself, with life, liberty, property and all those who are enjoying them with us; thus absurdly sacrificing the end to the means."
- Thomas Jefferson