Ryan Seacrest is an amazing host ... a practical joker!

During last night's American Idol taping, Seacrest walks over to his girlfriend Julianne Hough in the audience and says:

    "Julianne would you take the mic for a second. There's something that's been on my mind for a while."

After reaching into his pocket for what we thought was going to be an engagement ring, Ryan says to Julianne:

    "No, it's not that. It's a question I've been meaning to ask you and I don't want you to feel uncomfortable. Will you...give this note I wrote to Tom Cruise? I'm such a big fan -- I loved him in Cocktail."

Julianne's reaction ... "Oh, God." What a tease!