So the party (2 rogues, a sorcerer and a druid) had just encountered a boss at the end of a Dungeon that they were meant to run from and come back to kill later in a nemesis storyline, with plenty of emotion, revenge, and all-round anger, in the form of a massive, giant cobra that the DM may have gently edited the stats of, the DM's exact words were 'it's eye is about as tall as the dragonborn' (dragonborn being easily 7 foot tall). The party is trying to figure out how to run with no casualties, when one of the rogues tells the others to distract the snake and slips into some shadows, making a good enough roll that the snake doesn't notice or care. As the party gets flung around and almost killed by the snake, the rogue slowly creeps up the back of the snake, making good enough rolls and going slowly enough that the snake is too distracted by the fight to notice.
As the others are about to die, the rogue is right on top of the snakes head, and stands completely upright
Rogue: "So the snake's eye is bigger than I am"
Rogue: "I'd like to roll to drop off of the snake's head, and stop myself from falling by sticking my shortsword into its eye."
Two high acrobatics and attack rolls later, the rogue is hanging off of the hilt of his shortsword as the half-blind snake thrashes trying to dislodge him.
The rogue's next turn rolls around, and the entire table goes silent
Rogue:" I'd like to jump into its eye to get to the brain"
Two more unfortunate rolls later, one of them a nat 20, and the rogue is now suffocating, with the rest of the party standing well back and just watching the snake angrily butt it's head against things trying to get the rogue out. Not only does the snake fail, it rolls and nat 1 and propels the rogue into its brain, where the rogue proceeds to neatly cut through the brain stem, levelling up and utterly destroying the next planned session arc, and giving a group of level 4s thousands of gold pieces from the snake's hoard.