YOU COULD BE EXCOMMUNICATED FOR NOT WASHING YOUR HANDS

Talmud: Berachot 19a

R. Joshua b. Levi further said: In twenty-four places we find that the Beth din inflicted excommunication for an insult to a teacher, and they are all recorded in the Mishnah.

R. Eleazar asked him, Where? He replied: See if you can find them. He went and examined and found three cases: one of a scholar who threw contempt on the washing of the hands, another of one who made derogatory remarks about scholars after their death, and a third of one who made himself too familiar towards heaven.