There's an ancient song by Peter Paul and Mary, which lyrics include this -- "When will they ever learn?" -- and it has sudden relevance today because open-air markets were packed this weekend, and it's insane.

Check out the Studio City Farmers Market in L.A. Sunday, packed with scores of people crowding in ... some of whom were not wearing face masks. Again, the mask protects people from those who might have the virus, and people who know what they're talking about are urging everyone to wear anything other than the professional-grade masks when they're out and about.

And, look at this ... a line of people way closer than 6 feet apart are lining a sidewalk outside of a Hermosa Beach (SoCal.) bar, drinking, talking and violating social distancing rules.

L.A. Mayor Eric Garcetti announced a temporary suspension of all farmers markets until they could come up with a workable, safe plan. Fact is ... it's not happening in L.A. or elsewhere.

The good news ... Garcetti shut down the Brentwood Farmer's Market after there were insanely large crowds packed in last weekend, but the Market has now changed its ways ... and people are staying appropriately apart.