Reneé Rapp has no idea who Joe Rogan is ... and her fans are losing their minds.
Check out the viral clip from this week's "Call Her Daddy" podcast ... the singer and actress is asked a Rogan-related question by host Alex Cooper -- Rapp responds by asking "who the f***" Joe is ... she's then shocked he's the same height as she is when she Googles him.
Alex is clearly amused by this blunt question ands asks Reneé if she knows what "Fear Factor" or the UFC are.