I don't really have a nickname for any of them but for the longest time (particularly when I was much younger) I used to think Viconia was named VIctoria. Not sure why really...but anyways its kind of stuck in my mind.
Not for specific NPCs, but I call my Evil party (Dorn/Baeloth/Viconia/Montaron/Shar-Teel) "the Sword Coast Reavers" and my all-female Good/Neutral party (Dynaheir/Neera/Jaheira/Imoen/Branwen) "the Fighting Furies"...
I call them names but they're not exactly nicknames. The most common tend to be wanker and dickhead. These terms of affection are yelled at them when the pathfinding takes them somewhere I don't want them to be and are used most frequently when exploring the Firewine Ruins. "Oh for f**k's sake Khalid you total wanker! What are you doing over there?" "Jaheira you dickhead! You knew the trap was there so why did you walk into it?"
Comments
Viconia - Vicky.
Edwin - Eddy.
Ajantis - Isabelle (Adjani - french actress)
Montaron - Monty.
Branwen - Brownen.
Safana - Sahara.
Dynaheir - Dina.
Imoen - sis'.
Jaheira - big mama.
Khalid - pussy (rus: целкарик).
Neera - Njura (rus: Нюра).
Rasaad - Rasheed.
Dorn - Dron or Doorn.
Anomen - omnomnom.
Korgan - Morgan.
Alora - bushy (rus: лохматка).
Yoshimo - Yoshi or Kurasawa.
Valygar - Vin.
Xan - Han (rus: Хан).
Hexxat - Hexxit.
Hexxat - Hexxxat
Imoen - Imoen Heap
Safana - Banana
Irenicus - Jon Icarus
Sarevok - Saverok
Coran - Quran
Rasaad - Wazaap
Edwin - Badwin
Eldoth - Eww-doth
Permidion Stark - Spermidion Stark
Yoshimo - Yoshito
Female NPCs: "Lass"
Viconia: "Ma'am."
Ari (dutch pronouncion) the wingless,
Nalia d'Arse
Coward wizards