Act on Campus president Peter McCaffrey said the recent behaviour of Mr Edgar was "obscene" and the second-year marketing student should resign.
Mr Edgar has apologised for the language he used in a comment on Sir Roger's Facebook page on Wednesday night.
Mr McCaffrey said Mr Edgar also encouraged students to rip up photographs of retired Act MP Heather Roy, the architect of the contentious Freedom of Association Bill, during yesterday's protest outside the University of Otago Robertson Library opening.
"These personal attacks and hateful messages, committed by someone who claims to represent the views of all students, are completely inappropriate ... Mr Edgar should resign from his position of responsibility immediately," Mr McCaffrey said.
New Zealand Union of Students' Associations co-president David Do, who was at the Robertson Library protest, said Mr Edgar had apologised for his inappropriate language and had withdrawn the comments "almost immediately" from the internet.
The comments did not detract from the "broader issues" student associations faced from the threat of voluntary student membership, Mr Do said.
It is not the first time Act on Campus and Mr Edgar have clashed, after the OUSA president was allegedly assaulted by a member of the group at a publicity campaign against VSM last month.
