TL;DR version: I joined a game, got killed by a Sentry, activated an enemy Spy fake death on my second life, and the game said I got revenge on the Spy! I died only once!
Veeeery long version: I was playing Hoodoo on defense (first part, BLU still didn't make a single cap, about to make), decided to go Spy, we had none. As I quit a Teleporter that was just on the side of the cap, our Medic is headshoted, decided to go there and kill the Sniper that did this. After going there, I saw the enemy Medic standing still and healing someone. On my mind "Screw the Snipers, screw the fact they have a Sentry, let's kill the Medic!". Killed the Medic, Sentry destroyed me. Since someone else also decided to go Spy during this, I went Soldier. They actually made the cap, destroyed the Teleporter, had to walk. As I went to that tunnel on the left, often used by classes who don't use the main route, but like to attack the enemies back (Scout, Pyro and on this case, Spy) I see a friendly Spy, but shoot a rocket at him to Spycheck. Bam, it was an enemy Spy, since he died on my first shoot, I decided to continue to walk foward to see if he was a Dead Ringer. Only then I realized the revenge cue was playing, and the game said I got revenge on him! What the heck? I died by a Sentry on my first life, and only once! BTW, he was in fact, a Dead Ringer. What happened????
Sorry for using GameFAQs as a diary, thing is, I never saw someone talking about such a glitch...