Avril Lavigne goes braless beneath a see-through top as she and Mod Sun head to a friend's house

Avril Lavigne shows rocker side in vintage Slayer T-shirt during coffee run with Mod Sun in Malibu

Avril Lavigne flashes midriff as she and Mod Sun twin in black on date night in Malibu

Avril Lavigne rocks a coat while Mod Sun opts for an Elmo shirt on date night in Santa Monica