There are many things that Benjamin says throughout the novel to illustrate his negativity and unpleasant, taciturn temperament. We learn about this early in the book. In chapter one he is described as bad tempered and only talks when he wants to make a cynical remark. He is purported to have said, for example, that God had given him a tail to keep the flies off but that he would just as much have preferred no tail and no flies. His statement means that he does not see the benefit in anything, no matter how good it may seem.
The quote is significant in that it indicates that Benjamin is unaffected by the events around him. He stands aloof and only does what is necessary. He seldom comments about the changes in the commandments or the pigs adopting human characteristics. He even refuses to comment about the wholesale slaughter of so-called traitors by Napoleon's dogs. In this instance, Clover asks him to read the commandment about the killing of animals, and he refuses. She has to ask Muriel the goat to read the commandment to her.
The fact that Benjamin never laughs because he never sees anything funny to laugh at further alludes to his bad temper. He is sour and grumpy and seems to accept his destiny. This acceptance is illustrated by his remark that "donkeys live a long time." Evidently, the suggestion is that he will outlive all the animals and will best know whether life, due to all the changes on the farm, will be better or not.
A further example of his cynicism exists in the remark that "windmill or no windmill, life would go on as it always did—that is, badly" when the animals are asked to vote in favor of or against the building of a windmill. His demeanor, overall, expresses the skepticism that many of the Russian middle class expressed about Stalin's reconstruction policies after the revolution.
In chapter ten Benjamin expresses the belief that hunger, hardship, and disappointment are the unalterable laws of life. This statement probably best encapsulates his disenchantment about the ongoing changes on the farm. His apathy comes across as a protective mechanism. If one does not raise one's expectations or express hope for the better, the chances of being disappointed are, essentially, nil. Benjamin is, in effect, a symbol for the foolishness of hope.
At the beginning of the novel we are introduced to all the animals. The reader is told that, "Benjamin is the oldest animal on the farm, and the worst tempered. He seldom talked and when he did it was usually to make some cynical remark - for instance, he would say the God had given him a tail to keep the files off, but that he would sooner have had no tail and no flies."
We also read that Benjamin never laughs. He is the only animal on the farm that never laughs. When the animals asked him why he never laughed Benjamin replies, "I didn't see anything funny."
There is more information on Animal Farm at the link listed below.