It means Be quiet in a ruder tone or like you're being surprised about something.
"And then- Blah blah blah blah"
"Shut up."
Or
"I got into 100% on that test that everyone failed."
"Shut up! No way. You're telling me you got 100% on that test? Shut up."
Glenice's favourite 2 words when we either roast her or act dirty minded around her
"I want tic tacs"
I got a tic tac right here đ
"shut up" *shakes head while crossing arms*
Doesnât mean off my dick at all
Milan tried using âshut upâ as another way to say off my dick.