This describes the act of ejaculating inside your partner prior to them conducting an extended period of strenuous activity like running a marathon or relocating a fish pond.
By the third hour of slogging in the sun, the fluid leaking into their underwear is known as a Spanish Breakfast. It is visual likened to a poorly prepared omelette and the ingredients vary depending on the hygiene of the ejaculatee.
I got home from gym last night and my skants were a Spanish breakfast. Even the dog was gagging.