Edward Drinker Cope and Othniel Charles Marsh
Cope, the "boy genius" of paleontology, and Marsh, an older, richer fossil collector, first met in 1863. They quickly bonded over their interest in hunting down the world's most exotic dinosaur bones. However, their shared ambition soon turned competitive and by the 1870s, they were openly slandering each other at every opportunity. Their research teams would even throw rocks at each other from neighboring dig sites. Real adult, guys.