A term used in gay circles, mainly in the 80's, referring to the act of one person, usually male, being anally ravaged by a group of men. It's essentially an Anabelle Chong played out by a group of queers, with one willing victim put through torment which takes weeks to recover from.
"Nigel had his first megatokyo last week. He was so off his face at the Market that he rounded up 12 of the regulars, took them back to his apartment, and took all of them in a 6 hour ordeal. I saw him yesterday, limping like a lame mule..."