Pull out a little notebook and write some shit in it, put it back in your pocket, look back at them quickly then continue as if nothing happened.

I like this! If they press you on an explanation for what you’re doing you could say “I have a bet going.” Glance down at the pad, perhaps flip a few pages, moving your pen like you’re counting, then say “It looks like I’m winning!” then smile.

If you don’t mine starting a fight you could even go with “I’m playing MAGA bingo. You could really help me out if you say something predictiably shitty about immigrants or perhaps something laughable about ‘small government’”.