APEMANTUS: Those healths will make thee and thy state look ill, Timon. (1.2.55-56)
It's no surprise that grumpy Apemantus doesn't agree with Timon giving all these parties; what is a surprise is the way he relates it to health and sickness. Right away, Timon's lifestyle is likened to sickness. Even if Timon doesn't know it yet, we know that his parties—or the consequences of these parties—will be like a disease that takes over his entire body.
These old fellows Have their ingratitude in them hereditary. Their blood is caked, 'tis cold, it seldom flows; 'Tis lack of kindly warmth they are not kind. (1.2.219-222)
When the blood is clotted, it cannot flow properly: Timon is saying that it's not really these old fellow's fault that they are irritable and cold—their blood made them that way. It's the start of his thinking about the body as a metaphor for the problems in society (or the social body—har har).
FLAMINIUS: Thou disease of a friend, and not himself! Has friendship such a faint and milky heart, It turns in less than two nights? O you gods, I feel master's passion! this slave, Unto his honour, has my lord's meat in him: Why should it thrive and turn to nutriment, When he is turn'd to poison? O, may diseases only work upon't! And, when he's sick to death, let not that part of nature Which my lord paid for, be of any power To expel sickness, but prolong his hour! (3.1.53-63)
When Lucullus rejects Timon's plea, Flaminius decides to have none of it. He doesn't just wish that bad things will happen to Lucullus; he describes—in vivid detail—how the meat from Timon's banquet should turn to poison in his stomach and torment him. It's a way of reminding Lucullus that just the other day, he feasted on Timon's meat and is probably still digesting it. Flaminius is basically telling Lucullus that he's an ungrateful hypocrite.
TIMON: Plagues, incident to men, Your potent and infectious fevers heap On Athens, ripe for stroke! Thou cold sciatica, Cripple our Senators, that their limbs may halt As lamely as their manners. Lust and liberty Creep in the minds and marrows of our youth, That 'gainst the stream of virtue they may strive, And drown themselves in riot! Itches, blains, Sow all the Athenian bosoms; and their crop Be general leprosy! Breath infect breath, That their society, as their friendship, may Be merely poison! (4.1.21-32)
As far as creepy curses go, this one is up there. Timon's wish for the society that hurt him isn't vague, but it is chock-full of disease and destruction. He's super specific in what he wants to happen to the bodies of everyone in Athens, perhaps so they can't continue to breed more infectious people?
TIMON: Be a whore still: they love thee not that use thee; Give them diseases, leaving with thee their lust. Make use of thy salt hours: season the slaves For tubs and baths; bring down rose-cheeked youth To the tub-fast and the diet. (4.3.84-88)
Lovely advice, Timon. This dude's got an appetite for revenge, and he's willing to pay prostitutes to infect his old friends, if that's what it takes. His dark plan shows us the level of his hostility toward them, but it also turns the tables on his friends. They might have once been a poison to him, but now he will infect them. We should point out that Timon also seems to think this would be a totally effective strategy, which suggests that he knows his friends go to prostitutes pretty often. That wouldn't be surprising: these guys all mix up money and friendship, so it seems about right that they would mix up sex and money, too. Nobody actually cares about anybody else; everyone's just buying the favors they want.
APEMANTUS: This is in thee a nature but infected; A poor unmanly melancholy sprung From change of fortune. Why this spade? this place? This slave-like habit? and these looks of care? Thy flatterers yet wear silk, drink wine, lie soft; Hug their diseased perfumes, and have forgot That ever Timon was. (4.3.203-209)
As much as this play talks about diseases, this is one of the few times it's not being literal. Timon may want to infect his friends with STDs, but Apemantus says that these people's very clothes are diseased. Why? Because these people continue to use other people and then throw them away. They're so bad that even their clothes are diseased. What's more: Apemantus thinks that Timon is infected, too. He accuses Timon of pretending to be grumpy when he really isn't. Apemantus thinks that Timon is putting on a big show... and maybe he is.
TIMON: Go, suck the subtle blood o' the grape, Till the high fever seethe your blood to froth, And so 'scape hanging: trust not the physician; His antidotes are poison, and he slays More than you rob. (4.3.431-435)
Man, Timon hates doctors. He tells the thieves that doctors lie more than they rob (which is, apparently, a lot). Timon believes that everyone and everything has turned to poison (it's not clear if he means that literally or not). It doesn't matter to Timon that doctors try to help prevent or treat disease; they are infected with the curse of humanity as well.
FLAVIUS: Is yond despised and ruinous man my lord? Full of decay and failing? O monument And wonder of good deeds evilly bestow'd! (4.3.461-463)
Flavius is taken aback when he first sees his old master. Flavius sees "decay and failing" in Timon, which suggests that Timon may already be dying. Maybe he's even already "dead," which would explain why Flavius has a hard time recognizing his master. Maybe Timon is deliberately forcing himself closer to the grave by crashing in a cave in the woods.
TIMON: Why, I was writing of my epitaph; It will be seen to-morrow: my long sickness Of health and living now begins to mend, And nothing brings me all things. Go, live still; Be Alcibiades your plague, you his, And last so long enough! (5.1.183-188)
Timon's words here have double meaning. First, he wants to rid the world of himself: he says he is like a disease that has caused grief. But he also wants to stop being sick (with pain and anger) himself. Getting rid of the Senators and bringing a sickness upon them and the rest of Athens is just gravy, really. Timon seems to just want to end it all.
APEMANTUS: (reading) Here lies a wretched corse, of wretched soul bereft: Seek not my name. A plague consume you wicked caitiffs left! (5.4.70-71)
Even in his epitaph, Timon wants to curse people with disease. This guy never quits. But he's also quick to point out his own miserable state as he decays in the tomb below. We'd like to know what kind of guy turns his epitaph into a guilt trip. Is this an admirable thing to do? It almost seems like Timon killed himself just to get back at his old friends. He's right: they are pretty nasty. But how much better is he, in the end? There's no right answer, but it's something Shakespeare probably wants us to think about.