For sunbathing in particular, do what Australia does:

- large scale public health campaigns on dangers of skin cancer. With a catchy song and slogan ("slip, slop, slap... Slip on a shirt, slop on sunscreen, slap on a hat")

- schools make it compulsory for kids to have hats in summer

- regulate tanning salons, promote fake tans in preference to sunbeds

- doctors check people for skin cancers during regular checkups

And over just a few years, being very brown quickly gets associated with being reckless and unhealthy.

In other words, regulate and educate