A woman so attractive you want to get pregnant to keep her.
The attractive level must surpass a desire to not have children. It will even override common sense however the woman must be a true beauty, not a decent one.
1. That Naomi Komaki is so hot I want to get her pregnant so she would have to stay with me. She's a real knock up knock out.
2. That knock up knock out is so hot I put a hole in the condom.
When you are banging a girl against a wall, then you perform a shocker and right as you are about to cum, you go back into her vagina, attempting to knock her up.
"Last night I was banging my big tiddy goth gf, when I accidentally did the Shock up Knock up."
A lovely little phrase with a dual meaning, both of which were coined by English speaking nations.
In the UK, it means "to knock on one's door in order to rouse them from their slumber". However, in the US, the younger and slightly more risqué cousin of the UK, it is a form of the verb phrase 'to knock up', which refers to the act of impregnating someone.
Remember to be mindful of your speech when travelling abroad.
British Man: "When would you like me to knock you up tommorrow?"
American Woman: "Who's gonna do what now!?"