Get, I do, a lot of referrer spam on my site. I’m pretty sure that every site gets referrer spam, they are ubiquitous. Usually I have already banned them and they are usually from Russia, such as xrus, dealing with lovely, nubile, young Russian women. These I treat like background noise: I glance at the error 403 and move on. Then occasionally, about once a month, I get a bona fide referrer spam marketing campaign, where someone really wants to make a negative impression on both my Google Analytics and myself. I then find and ban them.