Bieber hit the headlines this week for keeping fans waiting two hours at his first sold-out Believe show at the O2 Arena on Monday (March 4), causing outrage among parents.
Speaking of JB's antics at Russell Brand's Give It Up for Comic Reliefgig, Gallagher exclusively told MTV News: "Is it rock'n'roll to be two hours late? Depends what he was doing in those two hours. Was he snorting coke off prostitutes? Or was he playing bridge?"
When we told the rocker that rumours claim Justin was playing video games, the High Flying Birds star added: "Well that's not very rock'n'roll is it? My cat sounds more rock'n'roll than that."
Noel continued: "I don't know anything about him, I just know his name. I don't know anything about him.
"I know people really f**king hate him. I mean, kids love him. I don't even know who he is. No idea. And his name's Justin… whatever!"
Comedian John Bishop - who was also taking to the stage at the charity event - also referenced Bieber's lateness, joking: "He was supposed to be here tonight but we've told him the gig started at 1 o'clock… What a c**k!"