Hilary Duff My Sunday Funday ... His Muscles, My Ass and a Beach

11/13/2016 9:35 PM PST

Hilary Duff -- My Sunday Funday ... His Muscles, My Ass (PHOTO GALLERY)

Hilary Duff and her BF did some hardcore beach combing down in Mexico ... with minimal clothing, muchas gracias.

In case you forgot ... Jason Walsh made sure everyone in Puerto Vallarta knew he's a personal trainer by flexing through their day on the beach.

The couple looked to be searching for sea shells or something, but mostly bikini-clad Hilary just found an eyeful of his ass. Fun day, indeed.