Undertale Theory: Sans Might Have Pathological Demand Avoidance

There are evidences of Sans having this rare type of autism. Pathological Demand Avoidance is a real mental problem where everyday commands are resisted and uses social strategies to avoid doing the command. Once the command is said to the person with PDA, the person denies this by many alibis, whether that's playing pretend, changing the subject, or directly saying no. PDAers have trouble expressing empathy and may seem lazy and stubborn. They want to help, but because of a certain quirk in the brain, they can't and shutdown for a long time until doing the command.

It's a huge possibility Sans has this lifelong condition. Format is badly written on purpose to explain observations. You don't have to agree, and may label him PDA!Sans.

Don't be confused with Public Displays of Affection. This is the psychological term for the acronym PDA. It can also be known as EDA, Extreme Demand Avoidance.

There is a link in every comment section to learn more about this mental lifelong struggle, it can occur in all ages as a part of ASD.