We're not sure if Justin Bieber once had a traumatic experience with a belt that's since caused him to shun them -- all of them -- but one thing we do know is that he was wearing black undies during his Jacksonville, Fla. concert on Aug. 7, because they were on full display.

Maybe that was to draw attention from the fact that he might have lip-synced at least part of his show.

In the video you'll see the waist of his red leather leggings (aka diaper pants) refuses to stay where it belongs, so in pretty short order, Justin's entire backside makes an appearance.

Barely a moment goes by when he's not tugging on the pants somehow, but we're not sure if he's pulling them up or down or sideways or what. How he dances in those things is a mystery, though we have to say it's a bit awkward to watch -- the Biebs has the moves, but they'd be hard for anyone to pull off with a bunch of baggy leather around their knees.

But really, a shirtless Justin Bieber losing his pants isn't all that rare these days. What people are really buzzing about is that a couple minutes in to the video, he launches into 'Boyfriend' -- and at one point, he's dancing and moving his mouth, but the mic isn't anywhere near it.

In fairness, most performers who both sing and dance use backing tracks, but they aren't normally quite so blatant about it.

Maybe that's why his concerts lately haven't gotten great reviews -- earlier this month, the Associated Press wrote, "During the opening up-tempo numbers, he seemed to be lip syncing and his sluggish, lazy dancing didn't match the oomph of the beats," and "Bieber phoned in a good amount during his show; at some moments, he even appeared bored."