- 9/11 Truthers;
- Fathers' rights activists (this is probably the least known of the three; for a primer, go here).
On the other hand, it's impossible not to feel some empathy for the anti-vaccinationists, even while realizing that they must be mercilessly crushed. Their desire to find someone to blame and extract large cash settlements from that someone is fundamentally human (hmm, evolutionary psychology? Contemptible, but not top three material).
The 9/11 Truthers can't actually effect the world until they put down the bong; and once they quit smoking dope they discover that the towers really did fall because Muslim fanatics flew planes into them. Plus, they do provide hours of laughter, like the woman truther who, finally convinced that the government couldn't have wired explosives in the towers in the weeks leading up to 9/11, surmised that every skyscraper in the country must be wired with explosives during construction.
As a result, for having no redeeming value whatsover, fathers' rights activists are, of all the whiniest whiners who whine, the whiniest whiners of all.