Have you considered serving a zip bomb to this user agent?
I'm sure their crawler can handle a zip bomb. Plus it might interpret that as "this site doesn't have a robots.txt" and start scraping that OP is trying to prevent with their current robots.txt.
alt Hacker News
I'm sure their crawler can handle a zip bomb. Plus it might interpret that as "this site doesn't have a robots.txt" and start scraping that OP is trying to prevent with their current robots.txt.