When the significant other has not learned their lesson in life or used protection. One party or the other straight sent it.
Man :"That woman was so out of line when she cheated on me, I did an about face and got her pregnant, revenge baby."
Woman: "That fucking asshole gave me what I wanted after I cheated on him. Then he kept his mouth shut, played along and I threw him away. Then the mouther fucker surprises me, gets a good job , wants to be a family and marries me, then quits the job and is now jobless social shaming me some more, so I got pregnant again, revenge baby, because he didn't learn his lesson either, then divorced him."