Derek Hough and Hayley Erbert have been having the best time in Las Vegas, where they have been performing in the show, Derek Hough: No Limit.MORE: Derek Hough reveals relationship milestone with girlfriend Hayley ErbertThe celebrity couple had reason to celebrate over the weekend too, as they discovered that all the tickets for the upcoming week had sold out.Taking to Instagram, Derek shared a loved-up picture of the pair of them dancing at the Venetian in Las Vegas, and wrote: "SOLD OUT! Wow!