Players may play a character, but they are not the character. Remember not to take in-character grievances to personal, out-of-character attacks, nor to use out-of-character motivations and agendas to fuel in-character behavior. Even when your characters are bitter enemies, remember to be respectful towards the players and that the goal of your interactions with them should be to have fun.
If you don't like someone, don't get involved with them. There are enough players in the server to go around that you should not be obligated to RP with someone who you don't like, and RPing under a hostile OOC environment only breeds poor IC and OOC behavior, drama, and frustration especially if staff gets involved.
Any information your character has should be gained from IC sources that are not your alternate characters. Out-of-character information can be helpful to gain context as a player, but by no means should it be used to dictate any aspect of in-character behavior.