The Big Gangbang was the finale of Series 5 and the second of a two-parter beginning with The Pandorica Opens. It was penned by Stubborn Noodles and features Eleven, Amy Pond, Amelia Pond, Auton Rory and River Bong.
The title is basically a joke centred around the conception of River. BRAVO PERTWHEEZE.
The Doctor has been sealed in The Pandorica, a trap created by his greatest enemies - Daleks, Cybermen, Sontarans etc. River Song is trapped aboard the exploding TARDIS and Auton Rory has just shot and killed Amy. The TARDIS's explosion has wiped out the entire universe. All that's left is the Earth, the moon, a sun and the fez (and a shit episode).
How this is resolved Edit
The Doctor escapes the Pandorica because fuck you. Then they dick around in a museum and shoot Eleven's fez. Then a Dalek shoots him. He then flies the Pandorica into the TARDIS explosion which reboots the universe but erases him but Amy remembers him back into existence. Eleven then gets drunk and dances with some underage girls.
Basically commits the cardinal sin of a Moffat two-parter of being a 45 minute third act to the preceding part.
ayy it's pretty GOAT. Bravo Moff.