When the male of a species that uses sex for pleasure has gone without intercourse for such a lengthy time that the resultant discharge is akin to a turbo-powered firehose hooked to a vat of mayonnaise.
After Bobo the Wonder Chimp had been isolated for 8 years, his first sexual encounter resulted in a sexplosion which rocketed the unfortunate female chimp a distance of 200 yards directly into a meat grinder. The silver lining is, the resultant burgers were delicious.
When viewing or performing acts of the best intercourse that one has ever possibly had which results in a type of nuclear explosion between the legs of either gender or both.