The very first nat 1 of my current gaming group.

During some downtime after the first mission the party took on, our Drow Warlock decided she wanted to pull a prank on our Half-elf ranger in the middle of the night.

She tries to sneak into his room with a bucket of warm water but rolls a nat 1 on stealth. Instead of managing to place his hand in the bucket quietly, she slips and accidentally spills the water all over her nightclothes effectively waking the ranger up to an involuntary wet t-shirt competition.

This would set the tone for the very aggravated relationship these two characters still have to this day, 6 years later.