In the blogosphere a rant refers to highly derogatory or critical comments regarding a specific issue or subject. A rant is usually quite subjective in nature, and can be about just about anything — from a rant against big government to TV coverage of the Olympics. You can find sports related rants at Bleacher Report or movie related rants at Cinematical.
You will find commentary on another rant at Gawker and may find a rant or two in the comments on just about any blog posting. A tirade against rants would be a rant itself.