Size and Weight:
As spinosaurs--large, carnivorous dinosaurs with crocodile-like heads and jaws--go, Irritator wasn't any more "irritating" than any other genus. Rather, this predator acquired its name because its only existing skull had been touched up with plaster by an overeager fossil hunter, requiring paleontologist Dave Martill to spend long, tedious hours undoing the damage.
As you may already have guessed, Irritator was closely related to its fellow South American theropod Spinosaurus, the biggest carnivorous dinosaur that ever lived--and it may yet wind up being assigned as a species of yet another South American spinosaur, Angaturama. By the way, the last name of the only known species of Irritator is "challengeri," after the lead character in Sir Arthur Conan Doyle's novel The Lost World.