When Justin Bieber made his appearance on The Late Show Thursday night in support of his new release Believe, he probably didn't anticipate having a skirmish with David Letterman over a tattoo, of all things.

However, that's just what happened, when Letterman spotted Bieber's latest ink--the title of his new album--on the singer's forearm. Doing his best cranky dad voice, Letterman groaned, "Oh God, how many do you have?"

Bieber attempted to explain that the tattoo was a special way to commemorate the new record, when Letterman suddenly pounced--grabbing his arm roughly and growling, "Get that off there!"

Bieber winced in pain and hollered, "Ay, ay, ay--this is brand new!" When Letterman released him, the star waved his hand dismissively and snorted, "Grandpas!"

That wasn't the last of the subject, however. Letterman wouldn't let off--asking first if Bieber's mother had a tattoo (no), and then if Dad had one.

After Bieber confirmed his pops indeed does have ink, Letterman looked resigned and said, "Just don't go nuts...more and more you see, like, the mural. Like the Sistine Chapel."

"I'm not going for the 16th Chapel," Bieber reassured him, inadvertently messing up the name of the famously frescoed landmark.

While the audience howled at Bieber's mistake, Letterman deadpanned, "Canadian high school." To which the Biebs responded with a steely glare.

Oh, burn! Better "believe" it: You can manhandle the fresh tattoo, but don't pick on the homeland!

Letterman had further fun with Bieber during the evening, teasing him about his hair, asking him about his college plans, and even breaking into a few opera stanzas with the superstar.

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