Fauxther
A male father-like figure with no genetic connection to a child. A fake dad. Someone else's baby mama's husband. A stepfather.
Larry: "Good job Susie...you played a great game! Let's go get some ice cream."
Susie: "Thanks Larry. I love you!"
Mom: "You're so sweet Larry. You're the best fauxther in the world!"

Timmy: "Look what I made you Mike! Happy Fauxther's Day!"
Mike: "Ahhh...thanks Timmy! What a beautiful card! Let's send a picture of it to your real dad in Jersey."