While looking at my sister's pictures of her recent trip to London, I came across this excellent caption:

When sunglasses like these go out of style, I'll wish I'd taken them off in more pictures.

What are the barriers to an efficient Coasean bargain if my sister's present-day choice of eyewear is imposing an intertemporal "internality" on her future self? Does this imply that we need a real-life "fashion police?"

*-Marginal Revolution.