Sarcasm is one of Max's most notable characteristics. Primarily, he uses it as a defense mechanism. As a huge, ungainly kid living in his grandparents' basement, he is pretty much one of society's outcasts. Sarcasm is a way for him to cope in a hostile, uncomprehending world. However, Max's sarcasm is not just directed at others, he also uses it against himself. There are numerous examples of different kinds of sarcasm in the first four chapters of Freak the Mighty.
Max starts right away in the very first line of the story:
I never had a brain until Freak came along and let me borrow his for a while, and that's the truth, the whole truth.
Of course, Max does have a brain, but, in comparison to Freak, he is not very smart. He is using sarcasm to exaggerate just how amazing he finds Freak's brain, how much he knows, and how incredibly wide-ranging his knowledge is.
Gram and Grim, bless their pointed little heads, they're my mother's people, her parents, and they figured whoa! better put this little critter with other little critters his own age, maybe it will improve his temper (Ch.1 p.1).
Max is showing us here how he feels about his grandparents. By referring to their "pointed heads," Max is suggesting that sure they are bright and they had the right motives in sending Max to the day care center, but they were making a big mistake in thinking it would curb his temper.
Grim has it fixed in his head I'm at a dangerous age and they need to keep me under observation. Like I might make bombs or start a fire. Or whack out the local pets with my trusty slingshot or whatever—except I never had a slingshot, it was Grim who had one when he was my age (Ch.2 p.5).
Max's grandpa is kind of worried that he might turn into some kind of psychopath, sitting down there in the basement all day, up to no good. Even worse, he might end up like his old man, and that is just way too horrible to contemplate. Max's use of sarcasm here gives us an insight into his lifestyle and character, as well as the relationship between him and his grandparents. Additionally, how does Max know that Grim used to use a slingshot when he was his age?
The proof is right there in the family photo album. You can see this blurry little miniature Grim with no front teeth, grinning at the camera and yanking back on this prehistoric slingshot. Good for whacking mastodons, probably (Ch.2 pp.5–6).
Mastodons are an extinct species of prehistoric elephants. Max is making a snarky reference to his grandpa's age and making him seem kind of hypocritical for using slingshots when he was around the same age as Max.
My brain is vacant, okay? I'm just this critter hiding out in the basement, drooling in my comic books or whatever. All right, I never actually drool, but you get the picture (Ch.2 p.6).
This is the image that Max has of himself. It is probably the same image that most other people would have too. Again, he is drawing attention to the fact that, before Freak came along, he was just this fat, slobby kid spending all day down in his grandparents' basement. He is highlighting the contrast in his character before and after he met Freak. After a while, though, Max gets bored with hanging out in the basement:
So finally I get bored in the down under and I'm hanging out in 'the so-calledback yard, your basic chunk of chain-link heaven (Ch.2 p.6).
Max's grandparents do not have a lot of money. They have a fairly ordinary house with just a small chunk of a backyard with a chain-link fence. Max seems almost embarrassed at his folks' place. However, he tries to minimize the embarrassment by the sarcastic use of the word "heaven" to describe the backyard.
Down in the basement, Max chats with Freak, overawed by his amazing erudition and knowledge. Max feels like a complete idiot, but he does not want to let it show, particularly when Freak tells him that books are a kind of truth serum that help you figure out what is real:
This time I don't say huh because then I might have to explain how I'm an L.D., and reading books is the last thing I want to do, right after trimming my toenails with a lawn mower, gargling nails, and eating worms for breakfast (Ch.4 p.19).
Once again, Max is using sarcasm as a protective shield. He knows he is not the brightest kid in the world; he knows he has learning disabilities, but he still does not want to come off like a complete idiot in the awesome presence of the mighty Freak and his even mightier brain.