What is an epikoros?
"AN EPIKOROS. Rab and R. Hanina both taught that this means one who disrespects a Talmid Chacham [erudite Torah scholar]. R. Johanan and R. Joshua b. Levi maintained that it is one who disrespects his neighbour in the presence of a Talmid Chacham. "I already mentioned that a lack of respect for Torah scholars is a sign of a lack of yir'at shamayim.
—B. Talmud, Seder Nezikin, tractate Sanhedrin, 99b