I don't know if this counts as a cool thing PCs have done, but it was a cool event.
In a D&D style world, the party was chased down by a huge army of bandits. Remember the rule: "You don't have to outrun the bad guys, you just have to outrun the Dwarves."
So all three Dwarven fighters were captured. The bandit tribes had a ritual; they would allow you to fight a combat (naked + weapon) against someone of similar (i.e, exact) abilities. If you won, they would allow you to be slaves.
Also in this world, if you were critted you rolled d20 vs. your Con or you were dead.
Dwarf 1: walks up and rolls a crit on the first swing. Enemy dead, Dwarf becomes slave.
Dwarf 2: walks up and gets critted on the first swing. Dwarf dead.
Dwarf 3: walks up and proceeds to fight the longest combat I have ever, ever seen (lots of 2s, 3s, and 4s). After something like 40 rounds of piss poor die rolling, both the Dwarf and the bandit has 1 or 2 hp left (0 = dead). Both swing, both get hits. Roll initiative. Dwarf loses, Dwarf dead.