I've been riding bikes for over 50 years. I'm legally required to wear a helmet but I don't when I'm just poking along the local parks on the way to the shops. I could get fined :-(

There's a strong cycling culture around here. Some of them ride in packs on some major roads. I'd never do that, with or without a helmet. Recently there was a major incident. One death, a bunch injured. The dead one had their head severed. The helmet didn't help.

[edit: I usually do wear a helmet for any major ride]