The meanest fish in the small's would be the Jewel cichlid hands down. In the Mediums would be the Red Devil or Midas and in the Bigger class id vote the Dovii and the Jaguar cichlid however some other perty nasty cichlids would be the Red Terror, ive seen nasty Oscar's also, ive seen evil Jack dempseys and as for africans, all of those have some attitude also.