Sans is lazy but can be energetic at times, he loves sleeping and drinking. He usually likes to say mweh heh heh like his brother, Papyrus. Sans wears Papyrus' old hoodie but dyed it blue to fit his boots and his eyes, which are blue.
Sans wears Papyrus' old hoodie but dyed it blue because he prefers blue to orange/red. Sans also wears blue boots and shorts with fabric inside them for maximum comfort, usually when sleeping and/or drinking.
Inside sans' hoodie is his own, specially made battlebody for sentry duties, and because papyrus forced him to.