He's simply disappointed, because he's got to eat his body again.
This could be for one (or more) of the following reasons: 1 - it's the only thing Kyubey has been eating for some time now or 2 - it tastes horrible or 3 - Kyubey has a very sensitive tongue that just can't stand
his own taste. In case of 2 and 3 I also have to conclude, that Kyubey eats his spare bodies simply because he has to dispose of them.