Same thing I wore to my 21st birthday -- how crazy!

Kidding -- Madison Beer sexed it up at her big birthday bash last night at LA nightclub Delilah. And other than her sexy self, some pretty hot friends were in attendance ... including Hailey Baldwin! Of course hubby Justin Bieber is credited with discovering Madison back when she was 13. All these years later, Beer is signed to Epic Records and is a huge international superstar, and she can thank Biebs for all that!