The High Five of Doom is episode 47a of Rocko's Modern Life. In this episode Filburt is suspected by Rocko and Heffer of being an alien after they peek at Filburt's private journal that he accidentally left behind.
Heffer runs inside Chewy Chicken and finds Filburt writing in his journal. Heffer tries to read it, but Filburt snatches it out of his reach and leaves to get to his meeting. Little does he know, he had dropped his journal as he left. Heffer picks it up and tries to sneak away with it, only for Rocko to catch him by surprise. Rocko decides to take it from Heffer to keep it so he could return it to Filburt the next time he see it.
At Rocko's house, Rocko leaves the journal in the coffee table and is curious of what Filburt has written about him. But Rocko squelches himself and tries to get his mind off the journal. Eventually, however, he decides to read just one page, only to get interrupted by Heffer, who barges through the door begging to read the journal. So Rocko lets him see one page, not letting him know that he attempted to read a page out of the diary.
Heffer reads the second page titled The Earth Log of Filburt Shellbach, where Filburt has written that he is an alien. They eventually read through the story that tells how Filburt and his alien allies make their way to earth, using Chewy Chicken as their headquarters to devise an evil plan, which consists on the "Quarnozian High Five of Death," a high five that vaporizes any victim who returns the gesture. Rocko and Heffer are convinced that Filburt is an alien and arrive at Chewy Chicken, where Filburt is enjoying his lunch. Rocko and Heffer meet up with him and Heffer interrogates him, asking him why turtles are at Chewy Chicken. Filburt explains that it's the only place that serves lettuce with broccoli squeezings. Rocko and Heffer leave the restaurant and spot Filburt squirting mustard on his armpits, convinced that he is eating mustard through it.
They follow the turtle to his trailer home and find that he is wearing antennas in his head. They run away in fear and return to Rocko's house to read the last chapter of the journal. To their horror, they read that a wallaby and a steer have found out about his plans and must be destroyed. When Filburt arrives, Rocko and Heffer barricade the door and Heffer finds that Filburt is inside, oblivious to the fact that the turtle is already inside the house. Eventually, he finds out and becomes horrified. FIlburt finally comes across his journal and offers Rocko and Heffer a high five. The two take cover and tell Filburt that they thought that he was an alien. Filburt explains that he wrote the theories for a science fiction novel. He also elucidates that he put the TV antenna on his head for good reception and that he squirted mustard on his armpits in replacement for cologne. FIlburt offers Rocko and Heffer a high five, and the two are instantly vaporized in the process.
It is later revealed that everything that happened in the plot was all what Rocko and Heffer had been reading as they came to the conclusion. Rocko and Heffer then find that what they read really was a novel and that Filburt wouldn't high-five anyone to death. Nonetheless, they end up getting scared when the turtle comes around and they barricade the doors, much to Filburt's confusion.