Justin Bieber spends a lot of his down time kissing girlfriend Selena Gomez. However, part of his job is kissing other girls. His 'Mistletoe' costar, Ali Williams, dished the dirt of her lip lock with the Biebs -- and on what Gomez thought when she saw them do it!

Most girls would take off their earrings and throw down watching their boyfriends kiss another girl. However, Hollywood Life reports that Gomez was okay with the on-screen smooching. "It was totally professional, and I love Selena,” Williams gushed.

Gomez seems to be comfortable having her boyfriend interact with other ladies. In December 2011 when Bieber appeared on 'X Factor' with runner up and hardcore Belieber Drew, Gomez was both present and supportive. “I  didn’t meet Selena, I heard she was in the building while I was singing with Justin,” Drew said about the Dec. 14th pre-taped performance. “I was like, ‘Awkward!’”

If it was awkward singing with Bieber in front of Gomez, we can only imagine how awkward it must have been to make out with him! Did Williams have a similar experience?

Nope! “It wasn’t awkward at all,” she said. “He was so nice and relaxed. Justin was very respectful, so it was comfortable.” Hey, Ali Williams? That sound you just heard was the wooed and envious sigh of Beliebers everywhere.

Watch the Justin Bieber 'Mistletoe' Video