Perhaps because 'Spring Breakers' and dating a possible criminal wasn't enough for Selena Gomez to shed her good girl image, she decided to have a really tasteful pre-21st birthday party.

The Disney darling and pals went to see Busty Heart, whose claim to quasifame is smashing beer cans with her enormous rack. How refined!

Gomez and friends hit up Beacher's Madhouse in Los Angeles on Saturday (July 21), the night before she turned 21. She and her pals sat in the VIP section to see Busty's show, because even when the entertainment is trashy, the company's totes classy.

Her on-again off-again PR stunt boyfriend, Justin Bieber, wasn't on hand (he was too busy grinding on Gomez doppelgangers in Boston after his Beantown stop on his Believe tour to make it)-- but he was on her cake. Sources say photos of Gomez and Biebs were iced onto a leopard print birthday cake for the singer-actress.

Delicious?

Watch Busty Heart Break Beer Cans With Her Boobs