A psychological condition first theorized by Sigmond Freud resulting when a person needs perpetual simulation with their mouth. This is manifested from the oral stage of development, from birth-18 months, when breastfeeding occurs.
If a baby is weened either too early or too late in development, it's thought he will develop an oral fixation. This may contribute to behaviors involving the mouth such as smoking, alcholism, over-eating, talking too much, or having an abrassive or "biting" personality.
"Jane just never seems to stop bitching people out. Seems she has an oral fixation."