Kyle (Owen Wilson) and Peter (Ed Helms) are twin brothers who discover after their mother's wedding that their father wasn't who she claimed it was. They set out on "Operation Who's Your Daddy" to find their father, but it is no easy task, considering that their mother really got around back in the day.
This movie contains examples of:
- As Himself: National Football League quarterback Terry Bradshaw as the first potential father.
- Bittersweet Ending: Not only does Kyle and Peter's father remain unknown, it turns out their actual birth mother died in childbirth and given her backstory, their father was most likely a rapist. However, they each create a family of their own and get rich making a "positive messages" smartphone app together.
- Brother–Sister Incest: Peter thinks he may have hooked up with his sister when he sees the same woman at a wake for a man they believe to be their dad. He's wrong, and they get together in the end.
- Con Man: Roland claims that he has a side gig as a repossession agent. He's actually just a thief.
- Death by Childbirth: Kyle and Peter's birth mother died while giving birth to them.
- Gene Hunting: Kyle and Peter meet four potential dads throughout the course of the movie. They all turn out to be red herrings.
- God Was My Co-Pilot: The hitchhiker cryptically tells Kyle and Peter "You already know my name" when he drops them off. Turns out he's The Universe.
- I Was Quite a Looker: We're repeatedly told that Helen was apparently quite the Head-Turning Beauty when she was young.
- Magical Negro: The hitchhiker the brothers pick up halfway through the movie in rural New York. He's not only a Misunderstood Loner with a Heart of Gold (Peter was convinced that he was a Serial Killer), he is implied to be God.
- Parental Sexuality Squick: Peter doesn't take it well when someone recalls his mother as "a dick whisperer".
- Sex Goddess: Rod claims the young Helen was extremely good in bed, to the point he calls her a "Dick Whisperer". Peter doesn't like learning that.