The `America`s Got Talent` host - who married the `Hero` hitmaker in 2008 - tries to romantically sing his wife`s own songs to her but always ends up ruining them.
When asked if he ever sings to Mariah, Nick answered: "Absolutely, and I am the worst singer ever and I try to serenade her with her own songs and I mess up all the words and she just laughs."
The TV presenter also spoke about the vacancy for judges on `American Idol` - following the departures of Simon Cowell, Ellen Degeneres and Kara DioGuardi - and he thinks Mariah would be perfect for a spot on the panel of the pop star search show.
He added to US TV show `Extra`: "She`s a voice technician, people don`t really understand how her vocal chords work and how hard she actually works at it, so a show like that would give her a great opportunity to show people what it really takes to be one of the world`s best singers."
Nick, 29, previously revealed the 40-year-old singer often speaks about judging hopefuls on the series.
He said: "You know what? She talks about it. She says, `I would love to do that.`
"She is one of the greatest singers of our time; she would be great. I don`t know if she has enough time, though, but if they could work with her schedule, I know she would love to do `American Idol`."