In the 2011 movie David Tennant played Las Vegas showman and vampire expert Peter Vincent.
In this video Peter shuts down Charley (Anton Yelchin), pretending not to believe vampires exist. However later that evening, after he recognizes the vampire's insignia on the pictures Charley gave him, he has a change of heart.
Warning this video contains strong language and the video is short in accordance with the copyright holder's wishes.
Apologies if this video does not play in your country. Many thanks to the YouTube account Just Tennant for uploading the video.
Fright Night section of DavidTennantOnTwitter.com