Miley Cyrus -- I Was a Smart-Ass, Not a Stoner

Miley Cyrus was just being a "smart-ass" a week ago when she said she was a pothead ... this according to her rep.

The rep tells TMZ ... Miley was joking about the cake her friends got her for her 19th birthday when she said, "You know you’re a stoner when friends make you a Bob Marley cake. You know you smoke way too much f***in’ weed."

The rep says the Bob Marley cake was an inside joke ... Kelly Osbourne has been calling her "Bob Miley" since the infamous salvia incident that TMZ broke last year.

The rep says Miley is NOT a pothead ... and it was all meant in jest.