Necromania (3.5e Trait)
From D&D Wiki
You are (morbidly) obsessed with death and the undead and the living tends to be weary of you for that reason.
Benefit: You gain a +2 bonus to all Knowledge checks to indentify undead creatures and Charisma based checks used against intelligent undead.
Drawback: You suffer a -2 penalty to all Charisma based checks involving living creatures and NPCs that would normally be indifferent to you become unfriendly upon the moment they learn of your grotesque interests.
Roleplaying Ideas: Characters with such "refined tastes" are doubtlessly either a necromancer or on their way to becoming a necromancer, but may witnessed some great trauma in their past involving the death of loved ones and/or undead leading them to become deeply obsessed with the cause of their trauma later in their life. Most characters with this trait tend to not realize that obsessing over death or getting excited at the sight of a rotting zombie isn't normal. Characters that do though tend to feel like outsiders even among friends and often become secretive, possibly loners, keeping company with only those who'd understand. Most of the time those people are the dead.