Can taking a lot of tylenol (acetaminophen) pm cause bi polar moods to be more extreme?

I doubt it: Extreme reactions can include seizures and arrythmias but I am not aware of it worsening bipolar disorder.

Kills liver cells: Worst thing about tylenol (acetaminophen) is that taking as little as 3000 mg per day (6 extra strength pills) can cause fatal liver damage. Healthy adults who do not drink alcohol might be able to recover but still, this is the biggest risk of fatality for almost any drug currently on the market, let alone something available without prescription. I would worry more about liver than bipolar if taking a lot.

Maybe: There are reports that small doses of Diphenhydramine can impact frontal lobe function for days after a single use. This might impair your judgment particularly if you are taking psychotropic medications or alcohol. Impaired judgment can lead to increased anxiety which in turn can trigger bipolar meltdowns. I'd avoid first generation antihistamines if possible.