[salad77]

Sure, wait a month then go to a starbucks store and peacefully and politely hang out for a few hours without purchasing anything. If nothing happens up till then, try to use the restroom too. Then hang out some more before leaving.

If you don't spend the night in jail, then you have one data point suggesting not PR.

Have a reasonable sample of people repeat the experiment in multiple locations and multiple times and carefully record and report the results to you.

Collate the data points and report on the number of people arrested during the experiment.

Feel free to include Starbucks in a tweet about your results when you publish.

[fencepost]

If nothing happens up till then, try to use the restroom too. Then hang out some more before leaving.

This whole thing is going to have huge variation between locations. Suburban or drive - to locations often don't ever lock the bathrooms, while ones in cities are more likely to.