Why Rabbits Fight And Bite Each Other
No matter what many people might think, rabbits don't need 'friends' the same way people do. Rabbits are very picky about who their friends are. When they make friends, they make friends for life, but they can't be forced to make friends with just any rabbit, which is why you introduce rabbits at your own risk. People adopting rabbits when they already have one often take the first rabbit along to see how it gets along with the new rabbit. Like people, some rabbits make friends easily, others are less friendly.
If you already have two rabbits that are not getting along, some people recommend putting them in separate small cages and taking them for a drive in the car next to each other. A car journey is somewhat stressful for a bunny, and being taken for a car ride can sometimes help bond two rabbits together, in much the same way people do team building exercises to help them work better together.
Of course, all rabbits have minds of their own and not all of them will fall for team building exercises. If your rabbit is continuously aggressive towards your other rabbit, you may need to separate them. Rabbits can inflict nasty wounds on each other and they have notoriously soft skin that tears easily, so you don't want to leave two bunnies to simply beat each other up.
Depending on the age and gender of the bunnies, you may have preventable problems. For instance, if you have two un-neutered males, there is a good chance that they may become aggressive towards each other as they mature. You can tone down some of this aggression by having them neutered.
Similarly, a female rabbit may be aggressive towards a male if he is harassing her to mate and she does not want to. In general, it is always a good idea to have a pet rabbit neutered or spayed. Un-spayed female rabbits usually die before they are four years old due to cancer, and un-neutered male rabbits can have an unpleasant odor and be prone to aggression. There's no reason for a private owner to breed rabbits, rabbit breeding is not as easy at it looks, and if you do breed you have to deal with issues like pregnant doe health, deformed babies and care of the young. So get your bunnies fixed! They will have a longer and healthier life and they will be much friendlier to you and other rabbits.