Disposition is how an NPC feels about you on a scale from 0 to 100.

Things that effect disposition are:

PC ActionDefault ValueGame Setting Formula
Same Race5iDispRaceMod
Personality0.5 * (AttPer - 50)fDispPerMult * (AttPer - iDispPerBase)
Faction Reaction(FactionReaction * 5) * (0.5 + (Rank * 0.5))( Faction Reaction * fDispFactionMod ) * (fDispFactionRankBase + (Rank * fDispFactionRankMult))
Criminal Status Crime Level * fCrimeDispMod
Diseased-10fDispDiseasedMod
Attack NPC-20iDispAttackMod
Bargain1iDispBargainSuccMod
Failed Offer-1iDispBargainFailMod
Stealing-1 * Item ValuefDispStealing * Item Value
Pick Pocketing-25iDispPickPocketMod
Trespassing-20iDispTresspass
TauntingFrom Persuasion Formula 
IntimidationFrom Persuasion Formula 
BriberyFrom Persuasion Formula