Tylenol itself isn't.
You have to figure how good your liver's glutathione stores may be. Then you figure about a tenth of the acetaminophen will be metabolized to NAPQI (the toxic thing). But it may be more, or considerably less. Acute toxicity isn't going to happen with less than 150 mg Tylenol per kg body mass, and it may take as much as 500 mg/kg.
Then you have to figure what happens if you really, really poison your liver. About day 3 after ingestion, you begin to feel sick and nauseated. Later you're likely to develop ascites and portal hypertension, and at some point you're likely to have esophageal varices that bleed profusely, so you can die from puking up buckets of blood. Or you may go into a delirium, at which point somebody will probably call for help, so you can be treated and enjoy it all over again. But at some point, unless you get a liver transplant, you will die.