Quote 1
"Human beings have to have their sleep." (1.5)
Is Kafka suggesting here that Gregor turned into a bug because he didn't get enough sleep? That's a good one to try on your parents or anyone else the next time they try to wake you up early. In any case, you'll find Gregor making all kinds of statements in the story that are ironic because of the context. That is, what would normally be a obvious statement – everyone agrees that human beings need sleep – becomes absurd in view of the fact that Gregor is a bug. (This, by the way, is what literary critics call "dramatic irony.")
Quote 2
Gregor's legs began whirring now that he was going to eat […] "Have I become less sensitive?" he thought, already sucking greedily at the cheese. (2.7)
Gregor's new body responds in strange new ways to his needs. (Imagine how awkward it would be if your legs spun around every time you got hungry.) Before you dismiss Gregor's habits as another indication of his disgusting vermin-hood, take a look at the way the boarders eat in 3.10-11.
Quote 3
When Gregor Samsa woke up one morning from unsettling dreams [...] "What's happened to me?" he thought. It was no dream (1.1-2)
The philosopher René Descartes once wondered how it was possible to distinguish between dream and reality. His answer? God wouldn't be so cruel (read more). Kafka plays on the Cartesian reference here. How does Gregor know it's not just a dream? Isn't being a bug sure evidence that he's stuck in a dream? Would God be so cruel?
Quote 4
"The head of the firm did suggest to me this morning a possible explanation for your tardiness – it concerned the cash payments recently entrusted to you – but really, I practically gave my word of honor that this explanation could not be right" (1.19)
In addition to possible sexual deviance in Quote #1, Quote #2 suggests that Gregor may be guilty of misconduct at his firm. We never find out what really happened to those cash payments, although Gregor insists that he's done nothing irregular.
Quote 5
"Look how these roomers are gorging themselves, and I'm dying!" (3.11)
Here we have another reference to Gregor as "dying." The passage draws a contrast between the human roomers and Gregor in order to ask the reader whether it's OK to maintain human life over an insect's, even if the insect is your erstwhile son/brother.
Quote 6
That's all I'd have to try with my boss; I'd be fired on the spot. Anyway, who knows if that wouldn't be a very good thing for me. If I didn't hold back for my parents' sake, I would have quit long ago. (1.5)
The "that" that Gregor is referring to here is waking up late like the other traveling salesmen. Ironically, that's just what he's doing here, although we don't find out he's late until the next paragraph. Of course, he has a very good reason to be late – he's a vermin. But the transformation has the unintended consequence of fulfilling Gregor's wish to be rid of his job.
Quote 7
"Oh God," he thought, "what a grueling job I've picked! […] I've got the torture of traveling, worrying about changing trains, eating miserable food at all hours, constantly seeing new faces, no relationships that last or get more intimate." (1.4)
The life of a traveling salesman should look awfully good to someone who just got turned into a vermin, but that's not the case for Gregor. Gregor views the transient life of a traveling salesman as, well, dehumanizing. It's an asocial and physically grueling lifestyle.
Quote 8
"A man might find for a moment that he was unable to work, but that's exactly the right time to remember his past accomplishments and to consider that later on, when the obstacle has been removed, he's bound to work all the harder and more efficiently […] the traveling salesman, who is out of the office practically the whole year round, can so easily become the victim of gossip, contingencies, and unfounded accusations, against which he's completely unable to defend himself." (1.27)
In his eagerness to defend himself to the office manager, who's waiting outside his bedroom door unaware of what's happened, Gregor rattles off a great little speech about hard work. The speech is quite ironic because 1) it's hard to imagine what lessons can be learned from overcoming vermin-hood, and 2) the rumors about Gregor's delinquency really can't compare to the fantastic reality of what's happened to him.