Referral spam can also be annoying, with lots of plebs falling for it until they learn not to do it. Often referral spam is done because people genuinely like a product. And then there is the stupid chain mail stuff - help this kid in need by re-sharing this sob story ...
 

 Agree, although I feel muting those on the client is a bit simpler basis because you could just add most of that stuff into some word stop list.