The X-5 Unit is a biological weapon that appears in the movie Beavis and Butt-Head Do America. Dallas Grimes (an arms dealer) steals the weapon, then encounters Beavis and Butthead in a hotel room in Las Vegas after her husband, Muddy, has mistaken them for a pair of hitmen he has hired over the telephone to assassinate her. When the ATF track Dallas down, she hides ithe X-5 n Beavis' underpants in order to avoid being caught with it in her possession. She then tells Beavis and Butthead to meet her in Washington, D.C. Throughout the rest of the movie, Beavis and Butthead are completely unaware of the fact that they're carrying a deadly weapon; the only clue being that it is making Beavis' butt itch (He continues to scratch his butt throughout this episode). The ATF learn that Beavis and Butthead are in possession of the weapon, thus causing the two to become wanted criminals. Muddy Grimes (said husband of Dallas & also an arms dealer) also seeks the weapon. Muddy finds the boys unaware that it's nside Beavis' pants. Eventually, Beavis and Butthead make it to Washington, and before Dallas can meet up with them to recover the weapon, she is confronted in the parking garage by Muddy, who demands to know where the X-5 is. Later, Muddy and Dallas are arrested by the ATF. Faced with the possibility of a 60 year jail sentence, Dallas betrays Muddy, telling the ATF that she previously secreted the weapon "in some kid's pants." While masturbating in Mr Anderson's camper, Beavis is caught & thrown out without his pants. Tom Anderson then opens the camper door, telling Beavis to take his pants with him - ejecting them out the door, which causes the ATF to hurriedly go after them. The underpants are ripped open in the melee, with the consequence that the X-5 flies out of them. It lands safely in Butt-Head's hand, & not knowing what he has, he decides to give it to the ATF. The X-5 Unit is recovered, Anderson is accused of being Muddy and Dallas' accomplice & is subsequently arrested. Beavis and Butt-head become heroes.
- Beavis and Butt-head never knew what the X-5 Unit was. When the ATF demanded Beavis and Butthead to "hand over the Unit", the boys think the ATF wants to see their penis.
- Agent Bork stated that the X-5 Unit was an incomplete weapon because Dallas stole it while the Unit was being made.
- It is unknown what Dallas wanted to do with the unit, yet from what she was telling Muddy, it could be assumed she was going to sell it to a foreginer at the conference or perhaps just set it off.