Vanilla Ice -- Miley Cyrus is Right ... Justin Bieber Needs to Change

Vanilla Ice wants Justin Bieber to stop acting like a shirtless douchebag all the time and take Miley Cyrus' advice -- before his career becomes a big, fat joke.

Ice a.k.a. Rob Van Winkle thinks Miley was dead on when she told Rolling Stone ... she's been telling Bieber to put an end to the d-bag antics ... before people "think he's Vanilla Ice."

Rob was honored Miley name-dropped him as the bad example -- and paid respect with his own Miley-esque foot pic -- telling us he knows exactly where Biebs is coming from ... but only Justin has the power to make a change.

"It's like living an artificial life" Van Winkle says, adding, "when the dust settles, no one can figure it out or help you but yourself."

Word to your mother.