Was this riding shirtless, or riding with the wrong shirt?

I do a good portion of my riding wearing jeans, and I'd much rather crash wearing jeans than lycra.

I now wear high-vis shirts, vests, and coats, but rarely a jersey.

Just get a helmet and save the noggin. Also, keep in mind that a crash like the TDF crash may be a single person going down taking down a hundred behind him. Group dynamics can be very different than individual dynamics.

If you ride with a group ride unpaid, uninvited, without permission, and without signing the waiver... and take down the group... you won't be protected from liability. Nor would you have much of a liability claim against the group.