All good ideas but there are a few problems in this specific case.
I'm up in years (on the backside of 60) as is the hapless clerk who runs the express lane. She's a dear sweet (white) woman who's worked at the grocery store for a number of years, always ready with a kind word and smile when she sees me. I'd hate to get her in trouble and she's probably deathly afraid to confront some big strapping black abusing the rules.
And...this is probably the monkey-wrench in any plans to take action. I'm in Texas and the manager of the store is...a Mexican. It's been my experience that blacks and them are quick to cast aside their differences when "whitey" is involved. They constitute a formidable alliance by virtue of their sheer numbers here.
I carry but don't think the outcome would be in my favor. So I just let this type of creeping incivility pass.