I believe that was on purpose... I've not seen a set of chairs sturdy enough to hold up that much... aaaaa... yeah... you know
I've seen some great "deliberate" levi jokes over the years and even had one of my own for a while. Carl Balentine's were always classic... frequently when he told the girl to rise, he'd start floating up. At PCAM one year however, the sensation was quite strange... everyone's head started tilting back more and more in that the entire stage was raising up off the ground
Marcy and I experimented with a comedy Illusion act at one point, in which she was the fat B*tch in the audience giving me c*** (not the best) for using the cute "well endowed" girl on stage (her daughter, in fact) and challenged me to use her instead... Now Marcy was all of 5 foot 6 inches tall and weighs in at well over 300 pounds... you have to picture this...
There is a board sat across two short ladders... she situates herself upon said board as the audience begins to howl... seems the legs to the ladders are starting to bow and buckle... you can hear the not so subtle creaking of things.
I move to her feet and pull out the first ladder (actually, it was me and her two boys tugging on it, to pull it out from under her)... needless to say the lower body drops down (similar to what you see in that video) but then, just as the laughter subsides, the lone little ladder at her head collapses, sending here to the stage floor.
At this point I offer her the opportunity to "not suffer an further embarrassment" to which she refuses to leave, claiming that I'm the one that's getting embarrassed because I can't float her into the air.
The Gauntlet is thrown!
I remove my sport coat as the lights lower and dramatic music begins to play. I begin making the magical gestures in her direction, my body obviously exerting a great deal of energy as my shirt becomes rather pooled by perspiration, my brow and forehead likewise damp.
She suddenly begins to raise as I am seen straining, my face turning red... and...
BURRRRIP! 
I (seemingly) let loose with one hell of a fart. (The boys and their sister give me a seriously hard time at this point; one of them entering with a roll of toilet tissue... however, said "charm" seems to have put the fat lady to sleep... she's finally quiet)
We regain our composure and proceed... slowly but surely she is seen to raise inch by inch as my body becomes obviously soaked... in fact, the sweat is literally pouring from my forehead like a cascading water fall...
When we get her to about waist level we go to pass the hoop... which gets stuck!
I ultimately give up, lowering her back to the stage floor, where she lands with a quite audible thud.
I so miss that act, it was hilarious (the entire fat lady show, that is). We only performed if about half a dozen times but god was it fun.
