How do you slide this insane clamp off the exhaust pipe?

I took nut off and tried whacking it down the pipe, impossible
I think now use a torch and heat red hot to enlarge it, slide on new pipe, then use torch to shrink.

AND this is why these pipes are no longer useable, idiot exhaust worker cuts the old mufflers off, puts in a short stub of pipe and tries to weld it to the original now ruined pipe which he ruined, and can cause dangerous fumes to get into the car, and you can hear it leaking, all to save himself a few minutes.
Of course hiis weld is so bad and slaggy, all the slag falls out and look at the holes it leaves which leak exhaust out.
I have seen this other times on other cars. Rather than even unbolt a connection to a converter, on one car, someone cuts off the flange and attempts a joining weld. That makes it very harder and more expensive to fix.

I would rather they use SS  BAND CLAMPS, no welding needed to join lap or butt joints.

My pics too big to post, here is a Gphotos link
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Well, I slammed it down the old pipe, then I slammed it on the new pipe.  
What a glorified piece of GM engineering, no I am not surprised they did this.

And for some reason, not enough pipe length on the driver side to get into the muffler, perhaps it was slid in to the tailpipe too far, of course why I am not surprised the idiot muffler man who welded on the  extension after he cut the front pipe short  made it too long. Another example of stupidity.
So I bought a lap clamp on Amazon. Pipe diameter is 2 1/4". the lap clamp goes over both muffler and pipe.

And if you buy the walker forward pipes, one side has the flange, the other pipe does not, so if you need that flange it is Walker 31865, and O'reilly has the best price.

Got the new pipes on. Old muffler I used a band clamp and had to use RTV to seal it up.
Holds up to 700* and a muffler wont usually go over 500*.
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I used a sawzall to cut out the inner pipe from the inside. And I could see from previous hacking on the end, had a slit in the tube end, so this seals it best.

To make sure a good seal, I propped up tailpipe in the right position. Then smeared in the RTV and let it set overnight. Next AM, put some RTV on the band clamp in the center and along the aluminum curved spacer. Slipped it over the pipe and let it set 30 minutes, then tightened it up.
After a 5 hour cure, tested for leaks and it is good. It takes a 24 hour time for a full strength cure.

You do NOT need white muffler cement or any expensive product to seal leaks in exhaust, just the high temp Permatex RTV sealant. The RTV will stay flexible and wont crack loose. You could probably put it all over the slip joint and it would hold without even clamping, but I dont recommend that.

better then the hackjob that was there! hopefully it holds up long term for you.