A "Serial Forwarder" is that person who blows up your email in-box with every piece of internet humor that tickles their fancy. Often times this person is a good friend whom you don't want to upset by explaining just how annoying it is to have to clean their "cute jokes", chain emails, their "partisan political humor" and other asinine internet tidbits out of your in-box every day. Opening and viewing email from a "serial forwarder" can even put your computer at risk of a virus adding to the level of annoying achieved by these people.
Every day I get 2 to 4 stupid/annoying emails forwarded to me by a 67 year old man who is the father of a good friend of mine. Out of respect, I have not told this "serial forwarder" how annoying his forwarded emails are so I simply delete them without even looking at them.