A Groinal Exploder was a coercion device used by the BEGGs on Dave Lister. The BEGGs had originally found the device on a derelict space station. It contained explosives and threatened to explode Lister's genitals within a certain time limit if he did not follow through on his debts to the BEGGs.
When Lister made contact with a group of BEGGs on a remote moon, he spent an evening playing poker with them. He ended up losing both Starbug and Rimmer to his opponents and returning to Red Dwarf via jetpack.
In order to ensure his return with their new hologram, the BEGGs fitted Lister with a groinal exploder. It was a device designed to destroy the groin of the wearer once the timer ran out or if it was tampered with. It wrapped around Lister's waist and up his chest to a collar. The only word written on the exploder was ERRA. The Cat thought it was a pair of stylish new underpants. The Dwarfers could not remove it and had to try to trick the BEGGs into deactivating the exploder.
The BEGGs proved to be smarter than they looked and didn't fall for Lister's ploys. When all the BEGGs choked to death, a new plan was needed. After figuring out that the word ERRA meant the Erroneous Reasoning Research Academy, The Dwarfers headed there and found the exploder's inventor in stasis. Professor Irene Edgington, once she had been restored from an accidentally induced chimpanzee form to her human self, was quite happy to give them the deactivation code.
Unfortunately, Irene was an incompetent ERRAnaut and couldn't remember the sequence. The Greek letters Alpha, Beta, Gamma, Delta and Theta had to be entered in the correct order or detonation would occur. Assuming that the correct letter would be the only one she didn't mention, Kryten entered the first 3 letters correctly. When Irene insisted that she knew the last letter, Kryten reasoned that her name (Irene E) meant irony. Concluding that just this once she might be right, he successfully deactivated the exploder. ("Entangled", Series X)
- The ticker timer on the groinal exploder varies greatly throughout the episode, with it even reading "0:00" while still on the BEGG moon. Later on, during the keypad sequence, it actually ticks upwards from "6:27" to "7:58" and finally "8:24" before eventually appearing under one minute. Though, given this device was invented by Professor Edgington, this is perhaps not so surprising.
- Lister refers to the exploder as "The Knacker Attacker" and "The Ball Buster".