Why is this SF line funny or relevant?

I was watching SF in syndication (3 times in a row everyday here, plus 5 in a row on Wednesday), when I heard this from The Parking Space:

Mike (to Jerry): You're looking tremendous. What are you on some kind of regimen?

Jerry: Yeah, twenty-five percent bran flakes. The forty percent was too much so I found a store to mix it up special for me, they take it down another fifteen percent.

Mike (laughing way too loud and hard): Ha ha ha ha!!! That's killer! Killer! I love that! Ha ha ha!!! You gotta use that, that's a definite!! Ha ha ha!!!

I looked up the script since the line didn't seem funny or I thought I heard it wrong. Also, Jerry really hams it up with a big smile and I think he even gives Mike the elbow nudge. Then I am thinking maybe it is supposed to be not funny- and Mike, who said once that Jerry is a phoney, makes a big deal out of it- sort of emphasizing how Mike ONLY pretends that Jerry is funny and makes him laugh- but behind Jerry's back thinks he is not funny.

But then again, I originally thought this phoney question meant that Mike thinks Jerry's personality is phoney, not necessarily that Jerry's not funny or that his humor is somehow phoney.

What does anyone else make of this exchange? Thanks

Once Upon A Summertime, Just A Dream From Yesterday A.J. wrote:

Bran Flakes imply pooping, and pooping is always funny. Well, actually pooping is only 25 percent funny, but Seinfeld mixes it up special and that brings it up another 15 percent.

** Captain Infinity ...it's 10:00 ...do you know where your pants are?

"A.J." wrote in message news:[email]...

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Can I just say that you've given this WAAAY more thought than it ever should have been given?. ;)

After the suggestion of Mikes that Jerry is a phony, Jerry tells a lame joke to test Mikes reaction to see whether he would let on his thoughts to Jerry's face. Of course, there is also the way in which we visualise Jerry going up to someone and asking they reduce the proportion of bran in his bran flakes to allow a certain amount of roughage in his diet, but not too much.

[email] (A.J.) wrote in message news:...

[email] (A.J.) wrote in message news:...

I think Jerry was playing on (an actual) cereal called "40% bran flakes"...and he had a store bring it "down another fifteen percent"...that's the joke.