After paparazzi caught the singer and the Hills star kissing, the duo headed to Las Vegas this weekend, where Friday they had dinner at Aria's Union and later went to Haze nightclub, where they "were all over each other," a source tells PEOPLE.
On Saturday, they were spotted together at the grand opening party for Mario Barth's King Ink.
Both avoided the red carpet leading into the club, thereby sidestepping any questions from reporters. Sitting next to each other on the patio of the combo bar-and-tattoo-parlor, the two danced together, continually touching each other's arms and legs all through the night.
As the night wore on they became even more affectionate. At 1 a.m., Lavigne, 25, decided to get a tattoo on her wrist – of the number 30, accompanied by a lighting bolt. Beforehand, she and Jenner could be seen kissing several times.
Jenner, 27, later got a matching tattoo of a lightning bolt below his ear.