I have kept rubys on and off for years.
I found that having a couple of pairs or 2 males fine. Males will nearly always scrap between themselves and show the most amazing colours when doing so. They can show jet black with little reflective specs on the scales and a nice deep red head.
I have had no other problems with them nipping other fish other than sparring with other barbs that are similar eg. tiger's, narayani's, stoliczkanus's etc