301 response to a selection of very large files hosted by companies you don't like.
When their AWS instances start downloading 70000 windows ISOs in parallel, they might notice.
Hard to do with cloudflare but you can also tar pit them. Accept the request and send a response, one character at a time (make sure you uncork and flush buffers/etc), with a 30 second delay between characters.
700 requests/second with say 10Kb headers/response. Sure is a shame your server is so slow.