This is one of those impossible to answer questions. Everybody has a different levels of comfort and discomfort. What one person might think is the most unbearable pain another might say meh...
"Any society that would give up a little liberty to gain a little security will deserve neither and lose both."~Benjamin Franklin
"Laws that forbid the carrying of arms... disarm only those who are neither inclined nor determined to commit crimes . . . Such laws make things worse for the assaulted and better for the assailants; they serve rather to encourage than to prevent homicides, for an unarmed man may be attacked with greater confidence than an armed man."~Thomas Jefferson
So far the worst thing for me has been kidney stones...I have heard stomach cancer and third degree burns are worse, however.
But if you listen real close, you can hear them whisper their legacy to you. Go on, lean in. Listen, you hear it? - - Carpe - - hear it? - - Carpe, carpe Landīca, seize IT boys, make your lives extraordinary.
If I'm not mistaken the poison from a platypus is one of the worst pains available on the planet. It's toxin doesn't destroy cells or tissue, it just activates pain cells to an intense threshold, an effect that can last for days or longer. Because it's a very timid animal and only uses it's barbs defensively very few have ever been stung.
While both male and female Platypus are born with ankle spurs, only the male has spurs which produce a cocktail of venom, composed largely of defensin-like proteins (DLPs), three of which are unique to the Platypus. The defensin proteins are produced by the immune system of the platypus. Although powerful enough to kill smaller animals such as dogs, the venom is not lethal to humans, but is so excruciating that the victim may be incapacitated. Oedema rapidly develops around the wound and gradually spreads throughout the affected limb. Information obtained from case histories and anecdotal evidence indicates that the pain develops into a long-lasting hyperalgesia that persists for days or even months.
Hyperalgesia is an increased sensitivity to pain, which may be caused by damage to nociceptors or peripheral nerves. Temporary increased sensitivity to pain also occurs as part of sickness behavior, the evolved response to infection.