One day, I started a new campaign in which one character was a barbarian with Whirling Frenzy from Unearthed Arcana. He decided to create a quirk that he hated being attacked with magic, so he went into a frenzy whenever he made a saving throw against a spell. Unfortunately, a party member decided to Charm him for some silly reason, and he wound up killing him in one critical hit when he just meant to go into frenzy to teach him a lesson. Then the other characters drew their weapons and advanced, so the whirling frenzy guy killed them all. Later, he decided to commit suicide.
So that same night, we made a new campaign where the 3rd-level adventurers were defeated by 8 goblins (except the wilder), then totally defeated by an Astral Construct (except one character who decided to join the goblins rather than be slain and actually summoned the Astral Construct). Then the bad guy had the one last character throw the others in the derro pit, which caused him to regret his actions and jump down there to save them, where they all died.
This is probably the first time I've had a PC-death in the first session except the time that one PC made a chaotic-evil rogue without telling me, while the party had a paladin, a cleric of the god of paladins, a lawful good monk, among others. When the halfling stole from the party and attempted a poorly-rolled forgery check to put the blame for the kidnappings the party had been tracking on a PC wizard ("After careful perusal, you are pretty sure that this text was not written by Xanthar. Not only does it not resemble the angular script of his people, but you see some of the backwards-curling tails common of halflings). The monk attempted to chase and subdue the halfling, and he did catch up, being a monk, despite the halfling's magically-doubled movement speed. Escaping the monk's grapple with Escape Artist, the halfling defeated him in a duel and continued running, climbing up a tree as high as he could to try to make it out of arrow range. The paladin continually rolled terrible rolls with his bow, unable to hit the rogue, so the cleric pulled out his mace and slammed it into the tree in an attempt to flush the rogue out. When the cleric rolled a critical on this (yes, I know trees are normally immune to criticals), I told the halfling to make a DC 15 Climb check, and he failed by 10, falling to the ground. The fall killed him.
So PCs only die in the first session when the other players kill them, though the 8 goblins came close to a TPK.
