I still have a 5k pixel square blank white gif on my site for times like that (~4kB) that I sub in for anything that gets requested too often, or from particular places.
I was getting hotlinked from controversial sites a lot at one stage, and the common forum software they used didn't force image sizes. So a 5k pixel wide image pushed most of the content off the screen thanks to a centred element :)
I remember from a long time ago something about an image that was corrupted, and did some self referral internally so you could crash applications through out of memory issues even though the image was only a couple of kilobytes. I might have to find it again to serve to hotlinkers!
I was getting hotlinked from controversial sites a lot at one stage, and the common forum software they used didn't force image sizes. So a 5k pixel wide image pushed most of the content off the screen thanks to a centred element :)